diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index db90db6fa4ab0..d8ec8bcb8df53 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -417,6 +417,8 @@ Bug Fixes in This Version
 - Fixed a regression in CTAD that a friend declaration that befriends itself may cause
   incorrect constraint substitution. (#GH86769).
 
+- Fixed an assertion failure on invalid InitListExpr in C89 mode (#GH88008).
+
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index a5fe83a539aaf..77150a318ee47 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -55,6 +55,7 @@
 #include "clang/Sema/Scope.h"
 #include "clang/Sema/SemaBase.h"
 #include "clang/Sema/SemaConcept.h"
+#include "clang/Sema/SemaDiagnostic.h"
 #include "clang/Sema/TypoCorrection.h"
 #include "clang/Sema/Weak.h"
 #include "llvm/ADT/ArrayRef.h"
@@ -3427,7 +3428,8 @@ class Sema final : public SemaBase {
       bool ConstexprSupported, bool CLinkageMayDiffer);
 
   /// type checking declaration initializers (C99 6.7.8)
-  bool CheckForConstantInitializer(Expr *e, QualType t);
+  bool CheckForConstantInitializer(
+      Expr *Init, unsigned DiagID = diag::err_init_element_not_constant);
 
   QualType deduceVarTypeFromInitializer(VarDecl *VDecl, DeclarationName Name,
                                         QualType Type, TypeSourceInfo *TSI,
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 390da508518e1..745cf41e204e7 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -12671,7 +12671,7 @@ void Sema::CheckMSVCRTEntryPoint(FunctionDecl *FD) {
   }
 }
 
-bool Sema::CheckForConstantInitializer(Expr *Init, QualType DclT) {
+bool Sema::CheckForConstantInitializer(Expr *Init, unsigned DiagID) {
   // FIXME: Need strict checking.  In C89, we need to check for
   // any assignment, increment, decrement, function-calls, or
   // commas outside of a sizeof.  In C99, it's the same list,
@@ -12689,8 +12689,7 @@ bool Sema::CheckForConstantInitializer(Expr *Init, QualType DclT) {
   const Expr *Culprit;
   if (Init->isConstantInitializer(Context, false, &Culprit))
     return false;
-  Diag(Culprit->getExprLoc(), diag::err_init_element_not_constant)
-    << Culprit->getSourceRange();
+  Diag(Culprit->getExprLoc(), DiagID) << Culprit->getSourceRange();
   return true;
 }
 
@@ -13808,29 +13807,24 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
     // OpenCL v1.2 s6.5.3: __constant locals must be constant-initialized.
     // This is true even in C++ for OpenCL.
     } else if (VDecl->getType().getAddressSpace() == LangAS::opencl_constant) {
-      CheckForConstantInitializer(Init, DclT);
+      CheckForConstantInitializer(Init);
 
-    // Otherwise, C++ does not restrict the initializer.
+      // Otherwise, C++ does not restrict the initializer.
     } else if (getLangOpts().CPlusPlus) {
       // do nothing
 
     // C99 6.7.8p4: All the expressions in an initializer for an object that has
     // static storage duration shall be constant expressions or string literals.
     } else if (VDecl->getStorageClass() == SC_Static) {
-      CheckForConstantInitializer(Init, DclT);
+      CheckForConstantInitializer(Init);
 
-    // C89 is stricter than C99 for aggregate initializers.
-    // C89 6.5.7p3: All the expressions [...] in an initializer list
-    // for an object that has aggregate or union type shall be
-    // constant expressions.
+      // C89 is stricter than C99 for aggregate initializers.
+      // C89 6.5.7p3: All the expressions [...] in an initializer list
+      // for an object that has aggregate or union type shall be
+      // constant expressions.
     } else if (!getLangOpts().C99 && VDecl->getType()->isAggregateType() &&
                isa<InitListExpr>(Init)) {
-      const Expr *Culprit;
-      if (!Init->isConstantInitializer(Context, false, &Culprit)) {
-        Diag(Culprit->getExprLoc(),
-             diag::ext_aggregate_init_not_constant)
-          << Culprit->getSourceRange();
-      }
+      CheckForConstantInitializer(Init, diag::ext_aggregate_init_not_constant);
     }
 
     if (auto *E = dyn_cast<ExprWithCleanups>(Init))
@@ -13963,7 +13957,7 @@ void Sema::AddInitializerToDecl(Decl *RealDecl, Expr *Init, bool DirectInit) {
     // Avoid duplicate diagnostics for constexpr variables.
     if (!getLangOpts().CPlusPlus && !VDecl->isInvalidDecl() &&
         !VDecl->isConstexpr())
-      CheckForConstantInitializer(Init, DclT);
+      CheckForConstantInitializer(Init);
   }
 
   QualType InitType = Init->getType();
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index cabffa47c9318..7c3faba0f7881 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -7331,7 +7331,7 @@ Sema::BuildCompoundLiteralExpr(SourceLocation LParenLoc, TypeSourceInfo *TInfo,
     if (!LiteralExpr->isTypeDependent() &&
         !LiteralExpr->isValueDependent() &&
         !literalType->isDependentType()) // C99 6.5.2.5p3
-      if (CheckForConstantInitializer(LiteralExpr, literalType))
+      if (CheckForConstantInitializer(LiteralExpr))
         return ExprError();
   } else if (literalType.getAddressSpace() != LangAS::opencl_private &&
              literalType.getAddressSpace() != LangAS::Default) {
diff --git a/clang/test/Sema/recover-expr-gh88008-nocrash.c b/clang/test/Sema/recover-expr-gh88008-nocrash.c
new file mode 100644
index 0000000000000..5500b33dd0e85
--- /dev/null
+++ b/clang/test/Sema/recover-expr-gh88008-nocrash.c
@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 %s -verify -fsyntax-only -std=c90
+
+struct S {
+  int v;
+};
+
+struct T; // expected-note {{forward declaration of 'struct T'}}
+
+void gh88008_nocrash(struct T *t) {
+  struct S s = { .v = t->y }; // expected-error {{incomplete definition of type 'struct T'}}
+}