diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 7eb413885b8..a34ca2ab97c 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -610,9 +610,9 @@ c_type_tag (const_tree t)
     return NULL_TREE;
   if (TREE_CODE (name) == TYPE_DECL)
     {
-      /* A TYPE_DECL added by add_decl_expr.  */
-      gcc_checking_assert (!DECL_NAME (name));
-      return NULL_TREE;
+      if (!DECL_NAME (name))
+	return NULL_TREE;
+      name = DECL_NAME (name);
     }
   gcc_checking_assert (TREE_CODE (name) == IDENTIFIER_NODE);
   return name;
diff --git a/gcc/testsuite/gcc.dg/pr121506.c b/gcc/testsuite/gcc.dg/pr121506.c
new file mode 100644
index 00000000000..0d0664739ac
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr121506.c
@@ -0,0 +1,8 @@
+/* PR c/121506 */
+/* { dg-do compile } */
+
+#include <stdarg.h>
+
+struct A;
+void foo (struct A *);	/* { dg-message "previous declaration of 'foo' with type 'void\\\(struct A \\\*\\\)'" } */
+void foo (va_list);	/* { dg-error "conflicting types for 'foo'; have" } */