diff --git a/flang/docs/Extensions.md b/flang/docs/Extensions.md
index 6e34db182da7b..46ef8f07b4a8b 100644
--- a/flang/docs/Extensions.md
+++ b/flang/docs/Extensions.md
@@ -113,6 +113,13 @@ end
   in F'2023 subclause 19.4 paragraphs 6 & 8 should apply.  Since this
   compiler properly scopes these names, violations of these restrictions
   elicit only portability warnings by default.
+* The rules for pairwise distinguishing the specific procedures of a
+  generic interface are inadequate, as admitted in note C.11.6 of F'2023.
+  Generic interfaces whose specific procedures can be easily proven by
+  hand to be pairwise distinct (i.e., no ambiguous reference is possible)
+  appear in real applications, but are still non-conforming under the
+  incomplete tests in F'2023 15.4.3.4.5.
+  These cases are compiled with optional portability warnings.
 
 ## Extensions, deletions, and legacy features supported by default
 
diff --git a/flang/include/flang/Common/Fortran-features.h b/flang/include/flang/Common/Fortran-features.h
index dc50aa7f5c559..e5757468c0d84 100644
--- a/flang/include/flang/Common/Fortran-features.h
+++ b/flang/include/flang/Common/Fortran-features.h
@@ -45,7 +45,8 @@ ENUM_CLASS(LanguageFeature, BackslashEscapes, OldDebugLines,
     MiscSourceExtensions, AllocateToOtherLength, LongNames, IntrinsicAsSpecific,
     BenignNameClash, BenignRedundancy, NullMoldAllocatableComponentValue,
     NopassScalarBase, MiscUseExtensions, ImpliedDoIndexScope,
-    DistinctCommonSizes, OddIndexVariableRestrictions)
+    DistinctCommonSizes, OddIndexVariableRestrictions,
+    IndistinguishableSpecifics)
 
 // Portability and suspicious usage warnings for conforming code
 ENUM_CLASS(UsageWarning, Portability, PointerToUndefinable,
diff --git a/flang/lib/Semantics/check-declarations.cpp b/flang/lib/Semantics/check-declarations.cpp
index d2f0c839cb5eb..38cf14c503d25 100644
--- a/flang/lib/Semantics/check-declarations.cpp
+++ b/flang/lib/Semantics/check-declarations.cpp
@@ -3532,6 +3532,16 @@ void DistinguishabilityHelper::Check(const Scope &scope) {
 void DistinguishabilityHelper::SayNotDistinguishable(const Scope &scope,
     const SourceName &name, GenericKind kind, const Symbol &proc1,
     const Symbol &proc2) {
+  if (!context_.ShouldWarn(
+          common::LanguageFeature::IndistinguishableSpecifics)) {
+    // The rules for distinguishing specific procedures (F'2023 15.4.3.4.5)
+    // are inadequate for some real-world cases like pFUnit, which has
+    // some generic interfaces whose specific procedures are provably
+    // unambiguous, but fail all of the standard's criteria for being
+    // conformably distinct.  So the best we can do here is to emit optional
+    // portability warnings for such cases.
+    return;
+  }
   std::string name1{proc1.name().ToString()};
   std::string name2{proc2.name().ToString()};
   if (kind.IsOperator() || kind.IsAssignment()) {
@@ -3546,11 +3556,11 @@ void DistinguishabilityHelper::SayNotDistinguishable(const Scope &scope,
   parser::Message *msg;
   if (scope.sourceRange().Contains(name)) {
     msg = &context_.Say(name,
-        "Generic '%s' may not have specific procedures '%s' and '%s' as their interfaces are not distinguishable"_err_en_US,
+        "Generic '%s' should not have specific procedures '%s' and '%s' as their interfaces are not distinguishable by the incomplete rules in the standard"_port_en_US,
         MakeOpName(name), name1, name2);
   } else {
     msg = &context_.Say(*GetTopLevelUnitContaining(proc1).GetName(),
-        "USE-associated generic '%s' may not have specific procedures '%s' and '%s' as their interfaces are not distinguishable"_err_en_US,
+        "USE-associated generic '%s' should not have specific procedures '%s' and '%s' as their interfaces are not distinguishable by the incomplete rules in the standard"_port_en_US,
         MakeOpName(name), name1, name2);
   }
   AttachDeclaration(*msg, scope, proc1);
diff --git a/flang/lib/Semantics/expression.cpp b/flang/lib/Semantics/expression.cpp
index 0e200db5e6bd6..8d817f077880b 100644
--- a/flang/lib/Semantics/expression.cpp
+++ b/flang/lib/Semantics/expression.cpp
@@ -2644,7 +2644,7 @@ const Symbol &ExpressionAnalyzer::AccessSpecific(
 void ExpressionAnalyzer::EmitGenericResolutionError(
     const Symbol &symbol, bool dueToAmbiguity, bool isSubroutine) {
   Say(dueToAmbiguity
-          ? "One or more actual arguments to the generic procedure '%s' matched multiple specific procedures, perhaps due to use of NULL() without MOLD= or an actual procedure with an implicit interface"_err_en_US
+          ? "The actual arguments to the generic procedure '%s' matched multiple specific procedures, perhaps due to use of NULL() without MOLD= or an actual procedure with an implicit interface"_err_en_US
           : semantics::IsGenericDefinedOp(symbol)
           ? "No specific procedure of generic operator '%s' matches the actual arguments"_err_en_US
           : isSubroutine
diff --git a/flang/lib/Semantics/mod-file.cpp b/flang/lib/Semantics/mod-file.cpp
index d7d8b6ea0d44b..7072ddee18ebe 100644
--- a/flang/lib/Semantics/mod-file.cpp
+++ b/flang/lib/Semantics/mod-file.cpp
@@ -186,9 +186,12 @@ static void HarvestInitializerSymbols(
     } else if (const auto &generic{symbol->detailsIf<GenericDetails>()};
                generic && generic->derivedType()) {
       const Symbol &dtSym{*generic->derivedType()};
-      CHECK(dtSym.has<DerivedTypeDetails>());
-      if (dtSym.scope()) {
-        HarvestInitializerSymbols(set, *dtSym.scope());
+      if (dtSym.has<DerivedTypeDetails>()) {
+        if (dtSym.scope()) {
+          HarvestInitializerSymbols(set, *dtSym.scope());
+        }
+      } else {
+        CHECK(dtSym.has<UseErrorDetails>());
       }
     } else if (IsNamedConstant(*symbol) || scope.IsDerivedType()) {
       if (const auto *object{symbol->detailsIf<ObjectEntityDetails>()}) {
diff --git a/flang/test/Semantics/generic05.F90 b/flang/test/Semantics/generic05.F90
index d26d5c8feebc8..dcd040b55c409 100644
--- a/flang/test/Semantics/generic05.F90
+++ b/flang/test/Semantics/generic05.F90
@@ -1,4 +1,4 @@
-! RUN: %python %S/test_errors.py %s %flang_fc1
+! RUN: %python %S/test_errors.py %s %flang_fc1 -pedantic
 ! Check for distinguishability of defined I/O procedures defined within
 ! and outside their types.
 module m1
@@ -6,7 +6,7 @@ module m1
     integer n
    contains
     procedure :: readt1a, readt1b
-    !ERROR: Generic 'read(unformatted)' may not have specific procedures 'readt1a' and 'readt1b' as their interfaces are not distinguishable
+    !PORTABILITY: Generic 'read(unformatted)' should not have specific procedures 'readt1a' and 'readt1b' as their interfaces are not distinguishable by the incomplete rules in the standard
     generic :: read(unformatted) => readt1a, readt1b
   end type
   type t2
@@ -15,7 +15,7 @@ module m1
   type t3
     integer n
   end type
-  !ERROR: Generic 'read(unformatted)' may not have specific procedures 'readt2a' and 'readt2b' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'read(unformatted)' should not have specific procedures 'readt2a' and 'readt2b' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface read(unformatted)
     module procedure :: readt1a, readt2a, readt2b, readt3
   end interface
diff --git a/flang/test/Semantics/generic07.f90 b/flang/test/Semantics/generic07.f90
index e7486c02a7d2b..f3858cc4394ba 100644
--- a/flang/test/Semantics/generic07.f90
+++ b/flang/test/Semantics/generic07.f90
@@ -1,4 +1,4 @@
-! RUN: %python %S/test_errors.py %s %flang_fc1
+! RUN: %python %S/test_errors.py %s %flang_fc1 -pedantic -Werror
 module m1
   type :: t1
     sequence
@@ -74,7 +74,7 @@ program test
   interface distinguishable3
     procedure :: s1a, s1b
   end interface
-  !ERROR: Generic 'indistinguishable' may not have specific procedures 's2b' and 's2a' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'indistinguishable' should not have specific procedures 's2b' and 's2a' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface indistinguishable
     procedure :: s2a, s2b
   end interface
diff --git a/flang/test/Semantics/resolve17.f90 b/flang/test/Semantics/resolve17.f90
index a782a6a7ac3eb..498c20393d43b 100644
--- a/flang/test/Semantics/resolve17.f90
+++ b/flang/test/Semantics/resolve17.f90
@@ -1,4 +1,4 @@
-! RUN: %python %S/test_errors.py %s %flang_fc1
+! RUN: %python %S/test_errors.py %s %flang_fc1 -pedantic
 module m
   integer :: foo
   !Note: PGI, Intel, and GNU allow this; NAG and Sun do not
@@ -96,7 +96,7 @@ subroutine sb(y)
   end
 end
 subroutine s6
-  !ERROR: Generic 'g' may not have specific procedures 'sa' and 'sb' as their interfaces are not distinguishable
+  !ERROR: Generic 'g' should not have specific procedures 'sa' and 'sb' as their interfaces are not distinguishable by the incomplete rules in the standard
   use m6a, g => gg
   use m6b, g => gg
 end
@@ -180,7 +180,7 @@ subroutine g()
   end
 end module
 subroutine s9
-  !ERROR: USE-associated generic 'g' may not have specific procedures 'g' and 'g' as their interfaces are not distinguishable
+  !PORTABILITY: USE-associated generic 'g' should not have specific procedures 'g' and 'g' as their interfaces are not distinguishable by the incomplete rules in the standard
   use m9a
   use m9b
 end
@@ -197,7 +197,7 @@ subroutine s(x)
 end
 module m10b
   use m10a
-  !ERROR: Generic 'g' may not have specific procedures 's' and 's' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g' should not have specific procedures 's' and 's' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g
     module procedure s
   end interface
diff --git a/flang/test/Semantics/resolve53.f90 b/flang/test/Semantics/resolve53.f90
index 22af2305fc339..5729db593146e 100644
--- a/flang/test/Semantics/resolve53.f90
+++ b/flang/test/Semantics/resolve53.f90
@@ -1,9 +1,9 @@
-! RUN: %python %S/test_errors.py %s %flang_fc1
+! RUN: %python %S/test_errors.py %s %flang_fc1 -pedantic
 ! 15.4.3.4.5 Restrictions on generic declarations
 ! Specific procedures of generic interfaces must be distinguishable.
 
 module m1
-  !ERROR: Generic 'g' may not have specific procedures 's2' and 's4' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g' should not have specific procedures 's2' and 's4' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g
     procedure s1
     procedure s2
@@ -25,7 +25,7 @@ subroutine s4(x)
 end
 
 module m2
-  !ERROR: Generic 'g' may not have specific procedures 'm2s1' and 'm2s2' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g' should not have specific procedures 'm2s1' and 'm2s2' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g
     subroutine m2s1(x)
     end subroutine
@@ -36,7 +36,7 @@ subroutine m2s2(x)
 end
 
 module m3
-  !ERROR: Generic 'g' may not have specific procedures 'm3f1' and 'm3f2' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g' should not have specific procedures 'm3f1' and 'm3f2' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g
     integer function m3f1()
     end function
@@ -79,7 +79,7 @@ subroutine m5s3(x)
 
 module m6
   use m5
-  !ERROR: Generic 'g' may not have specific procedures 'm5s1' and 'm6s4' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g' should not have specific procedures 'm5s1' and 'm6s4' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g
     subroutine m6s4(x)
     end subroutine
@@ -88,9 +88,9 @@ subroutine m6s4(x)
 
 module m7
   use m5
-  !ERROR: Generic 'g' may not have specific procedures 'm5s1' and 'm7s5' as their interfaces are not distinguishable
-  !ERROR: Generic 'g' may not have specific procedures 'm5s2' and 'm7s5' as their interfaces are not distinguishable
-  !ERROR: Generic 'g' may not have specific procedures 'm5s3' and 'm7s5' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g' should not have specific procedures 'm5s1' and 'm7s5' as their interfaces are not distinguishable by the incomplete rules in the standard
+  !PORTABILITY: Generic 'g' should not have specific procedures 'm5s2' and 'm7s5' as their interfaces are not distinguishable by the incomplete rules in the standard
+  !PORTABILITY: Generic 'g' should not have specific procedures 'm5s3' and 'm7s5' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g
     subroutine m7s5(x)
       real x(..)
@@ -100,7 +100,7 @@ subroutine m7s5(x)
 
 ! Two procedures that differ only by attributes are not distinguishable
 module m8
-  !ERROR: Generic 'g' may not have specific procedures 'm8s1' and 'm8s2' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g' should not have specific procedures 'm8s1' and 'm8s2' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g
     pure subroutine m8s1(x)
       real, intent(in) :: x
@@ -112,7 +112,7 @@ subroutine m8s2(x)
 end
 
 module m9
-  !ERROR: Generic 'g' may not have specific procedures 'm9s1' and 'm9s2' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g' should not have specific procedures 'm9s1' and 'm9s2' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g
     subroutine m9s1(x)
       real :: x(10)
@@ -124,7 +124,7 @@ subroutine m9s2(x)
 end
 
 module m10
-  !ERROR: Generic 'g' may not have specific procedures 'm10s1' and 'm10s2' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g' should not have specific procedures 'm10s1' and 'm10s2' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g
     subroutine m10s1(x)
       real :: x(10)
@@ -144,7 +144,7 @@ subroutine m11s2(x)
       real, allocatable :: x
     end subroutine
   end interface
-  !ERROR: Generic 'g2' may not have specific procedures 'm11s3' and 'm11s4' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g2' should not have specific procedures 'm11s3' and 'm11s4' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g2
     subroutine m11s3(x)
       real, pointer, intent(in) :: x
@@ -156,11 +156,11 @@ subroutine m11s4(x)
 end
 
 module m12
-  !ERROR: Generic 'g1' may not have specific procedures 's1' and 's2' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g1' should not have specific procedures 's1' and 's2' as their interfaces are not distinguishable by the incomplete rules in the standard
   generic :: g1 => s1, s2  ! rank-1 and assumed-rank
-  !ERROR: Generic 'g2' may not have specific procedures 's2' and 's3' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g2' should not have specific procedures 's2' and 's3' as their interfaces are not distinguishable by the incomplete rules in the standard
   generic :: g2 => s2, s3  ! scalar and assumed-rank
-  !ERROR: Generic 'g3' may not have specific procedures 's1' and 's4' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g3' should not have specific procedures 's1' and 's4' as their interfaces are not distinguishable by the incomplete rules in the standard
   generic :: g3 => s1, s4  ! different shape, same rank
 contains
   subroutine s1(x)
@@ -209,7 +209,7 @@ module m14
     module procedure f1
     module procedure f2
   end interface
-  !ERROR: Generic 'OPERATOR(+)' may not have specific procedures 'f1' and 'f3' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'OPERATOR(+)' should not have specific procedures 'f1' and 'f3' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface operator(+)
     module procedure f1
     module procedure f3
@@ -218,7 +218,7 @@ module m14
     module procedure f1
     module procedure f2
   end interface
-  !ERROR: Generic 'OPERATOR(.bar.)' may not have specific procedures 'f1' and 'f3' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'OPERATOR(.bar.)' should not have specific procedures 'f1' and 'f3' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface operator(.bar.)
     module procedure f1
     module procedure f3
@@ -260,12 +260,12 @@ module m15
     procedure s1
     procedure s2
   end interface
-  !ERROR: Generic 'g2' may not have specific procedures 's1' and 's3' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g2' should not have specific procedures 's1' and 's3' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g2
     procedure s1
     procedure s3
   end interface
-  !ERROR: Generic 'g3' may not have specific procedures 's4' and 's5' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g3' should not have specific procedures 's4' and 's5' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g3
     procedure s4
     procedure s5
@@ -285,17 +285,17 @@ module m15
     procedure s8
     procedure s9
   end interface
-  !ERROR: Generic 'g7' may not have specific procedures 's6' and 's7' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g7' should not have specific procedures 's6' and 's7' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g7
     procedure s6
     procedure s7
   end interface
-  !ERROR: Generic 'g8' may not have specific procedures 's6' and 's8' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g8' should not have specific procedures 's6' and 's8' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g8
     procedure s6
     procedure s8
   end interface
-  !ERROR: Generic 'g9' may not have specific procedures 's7' and 's8' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g9' should not have specific procedures 's7' and 's8' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g9
     procedure s7
     procedure s8
@@ -339,7 +339,7 @@ module m16
     procedure, nopass :: s2
     procedure, nopass :: s3
     generic :: g1 => s1, s2
-    !ERROR: Generic 'g2' may not have specific procedures 's1' and 's3' as their interfaces are not distinguishable
+    !PORTABILITY: Generic 'g2' should not have specific procedures 's1' and 's3' as their interfaces are not distinguishable by the incomplete rules in the standard
     generic :: g2 => s1, s3
   end type
 contains
@@ -368,7 +368,7 @@ module m17
     procedure s1
     procedure s2
   end interface
-  !ERROR: Generic 'g2' may not have specific procedures 's3' and 's4' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g2' should not have specific procedures 's3' and 's4' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g2
     procedure s3
     procedure s4
@@ -377,17 +377,17 @@ module m17
     procedure s1
     procedure s4
   end interface
-  !ERROR: Generic 'g4' may not have specific procedures 's2' and 's3' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g4' should not have specific procedures 's2' and 's3' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g4
     procedure s2
     procedure s3
   end interface
-  !ERROR: Generic 'g5' may not have specific procedures 's2' and 's5' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g5' should not have specific procedures 's2' and 's5' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g5
     procedure s2
     procedure s5
   end interface
-  !ERROR: Generic 'g6' may not have specific procedures 's2' and 's6' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'g6' should not have specific procedures 's2' and 's6' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface g6
     procedure s2
     procedure s6
@@ -439,7 +439,7 @@ module m19
     module procedure f1
     module procedure f2
   end interface
-  !ERROR: Generic 'OPERATOR(.bar.)' may not have specific procedures 'f2' and 'f3' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'OPERATOR(.bar.)' should not have specific procedures 'f2' and 'f3' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface operator(.bar.)
     module procedure f2
     module procedure f3
@@ -504,3 +504,21 @@ subroutine s2b(x)
     class(*), allocatable :: x
   end subroutine
 end module
+
+! Example reduced from pFUnit
+module m22
+  !PORTABILITY: Generic 'generic' should not have specific procedures 'sub1' and 'sub2' as their interfaces are not distinguishable by the incomplete rules in the standard
+  interface generic
+    procedure sub1, sub2
+  end interface
+ contains
+  subroutine sub1(b, c)
+    class(*) b
+    integer, optional :: c
+  end
+  subroutine sub2(a, b, c)
+    real a
+    class(*) b
+    integer, optional :: c
+  end
+end
diff --git a/flang/test/Semantics/resolve54.f90 b/flang/test/Semantics/resolve54.f90
index 8f48e3fe7dc33..b755bee947bac 100644
--- a/flang/test/Semantics/resolve54.f90
+++ b/flang/test/Semantics/resolve54.f90
@@ -1,4 +1,4 @@
-! RUN: %python %S/test_errors.py %s %flang_fc1
+! RUN: %python %S/test_errors.py %s %flang_fc1 -pedantic -Werror
 ! Tests based on examples in C.10.6
 
 ! C.10.6(10)
@@ -55,7 +55,7 @@ subroutine S3A(W, X, Y, Z)
 ! C.10.6(17)
 ! BAD4(1.0,2,Y=3.0,Z=4) could apply to either procedure
 module m4
-  !ERROR: Generic 'bad4' may not have specific procedures 's4a' and 's4b' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'bad4' should not have specific procedures 's4a' and 's4b' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface BAD4
     subroutine S4A(W, X, Y, Z)
       real :: W, Y
@@ -68,7 +68,7 @@ subroutine S4B(X, W, Z, Y)
   end interface
 end
 module m4b
-  !ERROR: Generic 'bad4' may not have specific procedures 's4b' and 's4a' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'bad4' should not have specific procedures 's4b' and 's4a' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface BAD4
     subroutine S4B(X, W, Z, Y)
       real :: X, Y
@@ -109,7 +109,7 @@ module FRUITS
 ! type(BOSC) :: A_BOSC
 ! BAD6(A_PEAR,A_BOSC)  ! could be s6a or s6b
 module m6
-  !ERROR: Generic 'bad6' may not have specific procedures 's6a' and 's6b' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'bad6' should not have specific procedures 's6a' and 's6b' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface BAD6
     subroutine S6A(X, Y)
       use FRUITS
@@ -123,7 +123,7 @@ subroutine S6B(X, Y)
   end interface
 end
 module m6b
-  !ERROR: Generic 'bad6' may not have specific procedures 's6b' and 's6a' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'bad6' should not have specific procedures 's6b' and 's6a' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface BAD6
     subroutine S6B(X, Y)
       use FRUITS
@@ -170,7 +170,7 @@ subroutine S7A(X, Y, Z)
 ! C.10.6(25)
 ! Invalid generic (according to the rules), despite the fact that it is unambiguous
 module m8
-  !ERROR: Generic 'bad8' may not have specific procedures 's8a' and 's8b' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'bad8' should not have specific procedures 's8a' and 's8b' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface BAD8
     subroutine S8A(X, Y, Z)
       real, optional :: X
diff --git a/flang/test/Semantics/resolve63.f90 b/flang/test/Semantics/resolve63.f90
index 5c4d9c69cd85d..1cb8a8584cc77 100644
--- a/flang/test/Semantics/resolve63.f90
+++ b/flang/test/Semantics/resolve63.f90
@@ -340,7 +340,7 @@ subroutine test
     call generic(null(), ip) ! ok
     call generic(null(mold=ip), null()) ! ok
     call generic(null(), null(mold=ip)) ! ok
-    !ERROR: One or more actual arguments to the generic procedure 'generic' matched multiple specific procedures, perhaps due to use of NULL() without MOLD= or an actual procedure with an implicit interface
+    !ERROR: The actual arguments to the generic procedure 'generic' matched multiple specific procedures, perhaps due to use of NULL() without MOLD= or an actual procedure with an implicit interface
     call generic(null(), null())
   end subroutine
 end
@@ -358,7 +358,7 @@ subroutine s2(af)
   end subroutine
   subroutine test
     external underspecified
-    !ERROR: One or more actual arguments to the generic procedure 'generic' matched multiple specific procedures, perhaps due to use of NULL() without MOLD= or an actual procedure with an implicit interface
+    !ERROR: The actual arguments to the generic procedure 'generic' matched multiple specific procedures, perhaps due to use of NULL() without MOLD= or an actual procedure with an implicit interface
     call generic(underspecified)
   end subroutine
 end module
diff --git a/flang/test/Semantics/resolve65.f90 b/flang/test/Semantics/resolve65.f90
index 583c5bca4b34e..4dd8c187ab0e9 100644
--- a/flang/test/Semantics/resolve65.f90
+++ b/flang/test/Semantics/resolve65.f90
@@ -1,13 +1,13 @@
-! RUN: %python %S/test_errors.py %s %flang_fc1
+! RUN: %python %S/test_errors.py %s %flang_fc1 -pedantic
 ! Test restrictions on what subprograms can be used for defined assignment.
 
 module m1
   implicit none
   type :: t
   contains
-    !ERROR: Generic 'assignment(=)' may not have specific procedures 't%assign_t4' and 't%assign_t5' as their interfaces are not distinguishable
-    !ERROR: Generic 'assignment(=)' may not have specific procedures 't%assign_t4' and 't%assign_t6' as their interfaces are not distinguishable
-    !ERROR: Generic 'assignment(=)' may not have specific procedures 't%assign_t5' and 't%assign_t6' as their interfaces are not distinguishable
+    !PORTABILITY: Generic 'assignment(=)' should not have specific procedures 't%assign_t4' and 't%assign_t5' as their interfaces are not distinguishable by the incomplete rules in the standard
+    !PORTABILITY: Generic 'assignment(=)' should not have specific procedures 't%assign_t4' and 't%assign_t6' as their interfaces are not distinguishable by the incomplete rules in the standard
+    !PORTABILITY: Generic 'assignment(=)' should not have specific procedures 't%assign_t5' and 't%assign_t6' as their interfaces are not distinguishable by the incomplete rules in the standard
     !ERROR: Defined assignment procedure 'binding' must be a subroutine
     generic :: assignment(=) => binding
     procedure :: binding => assign_t1
@@ -63,7 +63,7 @@ subroutine assign_t6(x, y)
 module m2
   type :: t
   end type
-  !ERROR: Generic 'assignment(=)' may not have specific procedures 's3' and 's4' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'assignment(=)' should not have specific procedures 's3' and 's4' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface assignment(=)
     !ERROR: In defined assignment subroutine 's1', dummy argument 'y' may not be OPTIONAL
     subroutine s1(x, y)
diff --git a/flang/test/Semantics/resolve96.f90 b/flang/test/Semantics/resolve96.f90
index 680d6b7bee55b..eea2eb470aa78 100644
--- a/flang/test/Semantics/resolve96.f90
+++ b/flang/test/Semantics/resolve96.f90
@@ -1,4 +1,4 @@
-! RUN: %python %S/test_errors.py %s %flang_fc1
+! RUN: %python %S/test_errors.py %s %flang_fc1 -pedantic -Werror
 
 ! Check distinguishability for specific procedures of defined operators and
 ! assignment. These are different from names because there a normal generic
@@ -18,7 +18,7 @@ module m1
   end type
   type :: t2
   end type
-  !ERROR: Generic 'OPERATOR(.foo.)' may not have specific procedures 's2' and 't1%p' as their interfaces are not distinguishable
+  !PORTABILITY: Generic 'OPERATOR(.foo.)' should not have specific procedures 's2' and 't1%p' as their interfaces are not distinguishable by the incomplete rules in the standard
   interface operator(.foo.)
     procedure :: s2
   end interface
@@ -39,7 +39,7 @@ module m2
     integer :: n
   contains
     procedure, pass(x1) :: p1 => s1
-    !ERROR: Generic 'assignment(=)' may not have specific procedures 't1%p1' and 't2%p2' as their interfaces are not distinguishable
+    !PORTABILITY: Generic 'assignment(=)' should not have specific procedures 't1%p1' and 't2%p2' as their interfaces are not distinguishable by the incomplete rules in the standard
     generic :: assignment(=) => p1
   end type
   type :: t2