diff --git a/include/swift/AST/Attr.def b/include/swift/AST/Attr.def
index 9c0eb1595c9e6..41f8385ad2763 100644
--- a/include/swift/AST/Attr.def
+++ b/include/swift/AST/Attr.def
@@ -492,9 +492,6 @@ SIMPLE_DECL_ATTR(rethrows, Rethrows,
 CONTEXTUAL_SIMPLE_DECL_ATTR(indirect, Indirect,
   DeclModifier | OnEnum | OnEnumElement | ABIBreakingToAdd | ABIBreakingToRemove | APIStableToAdd | APIStableToRemove,
   60)
-CONTEXTUAL_SIMPLE_DECL_ATTR(isolated, Isolated,
-  DeclModifier | OnParam | ABIBreakingToAdd | ABIBreakingToRemove | APIBreakingToAdd | APIBreakingToRemove,
-  103)
 CONTEXTUAL_SIMPLE_DECL_ATTR(async, Async,
   DeclModifier | OnVar | OnFunc | ABIBreakingToAdd | ABIBreakingToRemove | APIBreakingToAdd | APIBreakingToRemove,
   106)
diff --git a/lib/Sema/TypeCheckAttr.cpp b/lib/Sema/TypeCheckAttr.cpp
index ea5745c6a2b3a..a25d490cb9d15 100644
--- a/lib/Sema/TypeCheckAttr.cpp
+++ b/lib/Sema/TypeCheckAttr.cpp
@@ -160,7 +160,6 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
   IGNORED_ATTR(AtReasync)
   IGNORED_ATTR(ImplicitSelfCapture)
   IGNORED_ATTR(InheritActorContext)
-  IGNORED_ATTR(Isolated)
   IGNORED_ATTR(Preconcurrency)
   IGNORED_ATTR(BackDeployed)
   IGNORED_ATTR(Documentation)
diff --git a/lib/Sema/TypeCheckDeclOverride.cpp b/lib/Sema/TypeCheckDeclOverride.cpp
index dca95fce6864f..65d9364967ae8 100644
--- a/lib/Sema/TypeCheckDeclOverride.cpp
+++ b/lib/Sema/TypeCheckDeclOverride.cpp
@@ -1612,7 +1612,6 @@ namespace  {
     UNINTERESTING_ATTR(Nonisolated)
     UNINTERESTING_ATTR(ImplicitSelfCapture)
     UNINTERESTING_ATTR(InheritActorContext)
-    UNINTERESTING_ATTR(Isolated)
     UNINTERESTING_ATTR(NoImplicitCopy)
     UNINTERESTING_ATTR(UnavailableFromAsync)
 
diff --git a/lib/Serialization/ModuleFormat.h b/lib/Serialization/ModuleFormat.h
index a5e5cb1193dd5..5cb71e26fe33f 100644
--- a/lib/Serialization/ModuleFormat.h
+++ b/lib/Serialization/ModuleFormat.h
@@ -58,7 +58,7 @@ const uint16_t SWIFTMODULE_VERSION_MAJOR = 0;
 /// describe what change you made. The content of this comment isn't important;
 /// it just ensures a conflict if two people change the module format.
 /// Don't worry about adhering to the 80-column limit for this line.
-const uint16_t SWIFTMODULE_VERSION_MINOR = 843; // add OSLog string encoding
+const uint16_t SWIFTMODULE_VERSION_MINOR = 844; // remove IsolatedAttr
 
 /// A standard hash seed used for all string hashes in a serialized module.
 ///
diff --git a/test/Parse/macro_decl.swift b/test/Parse/macro_decl.swift
index 53f4afd5e5b66..7a8b801380e8f 100644
--- a/test/Parse/macro_decl.swift
+++ b/test/Parse/macro_decl.swift
@@ -44,7 +44,7 @@ func test() {
   dynamic #someFunc
 
   @CustomAttr
-  isolated #someFunc
+  #someFunc
 }
 
 public # someFunc // expected-error {{extraneous whitespace between '#' and macro name is not permitted}} {{9-10=}}