diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -406,6 +406,8 @@
   when it had been instantiated from a partial template specialization with different
   template arguments on the containing class. This fixes:
   (`#60778 <https://github.com/llvm/llvm-project/issues/60778>`_).
+- Fix crash on attempt to initialize union with flexible array member.
+  (`#61746 <https://github.com/llvm/llvm-project/issues/61746>`_).
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -811,7 +811,7 @@
       // order to leave them uninitialized, the ILE is expanded and the extra
       // fields are then filled with NoInitExpr.
       unsigned NumElems = numStructUnionElements(ILE->getType());
-      if (RDecl->hasFlexibleArrayMember())
+      if (!RDecl->isUnion() && RDecl->hasFlexibleArrayMember())
         ++NumElems;
       if (!VerifyOnly && ILE->getNumInits() < NumElems)
         ILE->resizeInits(SemaRef.Context, NumElems);
diff --git a/clang/test/Sema/flexible-array-in-union.c b/clang/test/Sema/flexible-array-in-union.c
new file mode 100644
--- /dev/null
+++ b/clang/test/Sema/flexible-array-in-union.c
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 %s -verify -fsyntax-only -DERROR
+// RUN: %clang_cc1 %s -verify -fsyntax-only -x c++
+// RUN: %clang_cc1 %s -verify -fsyntax-only -fms-compatibility
+// RUN: %clang_cc1 %s -verify -fsyntax-only -fms-compatibility -x c++
+
+// The test checks that an attempt to initialize union with flexible array
+// member with an initializer list doesn't crash clang.
+
+#ifdef ERROR
+// expected-error@+2 {{flexible array member 'x' in a union is not allowed}}
+#endif // ERROR
+union { char x[]; } r = {0};
+
+#ifndef ERROR
+// expected-no-diagnostics
+#endif // ERROR
+