diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 3d6b8f252a356478fbe515e677f313add0163ffb..b00a6cd5b8b33aa2ee9e2b4ae3a833668e926ec6 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -34473,14 +34473,32 @@ class_decl_loc_t::diag_mismatched_tags (tree type_decl)
 	 be (and inevitably is) at index zero.  */
       tree spec = specialization_of (type);
       cdlguide = class2loc.get (spec);
+      /* It's possible that we didn't find SPEC.  Consider:
+
+	   template<typename T> struct A {
+	     template<typename U> struct W { };
+	   };
+	   struct A<int>::W<int> w; // #1
+
+	 where while parsing A and #1 we've stashed
+	   A<T>
+	   A<T>::W<U>
+	   A<int>::W<int>
+	 into CLASS2LOC.  If TYPE is A<int>::W<int>, specialization_of
+	 will yield A<int>::W<U> which may be in CLASS2LOC if we had
+	 an A<int> class specialization, but otherwise won't be in it.
+	 So try to look up A<T>::W<U>.  */
+      if (!cdlguide)
+	{
+	  spec = DECL_TEMPLATE_RESULT (most_general_template (spec));
+	  cdlguide = class2loc.get (spec);
+	}
+      /* Now we really should have found something.  */
       gcc_assert (cdlguide != NULL);
     }
-  else
-    {
-      /* Skip declarations that consistently use the same class-key.  */
-      if (def_class_key != none_type)
-	return;
-    }
+  /* Skip declarations that consistently use the same class-key.  */
+  else if (def_class_key != none_type)
+    return;
 
   /* Set if a definition for the class has been seen.  */
   const bool def_p = cdlguide->def_p ();
diff --git a/gcc/testsuite/g++.dg/warn/Wmismatched-tags-11.C b/gcc/testsuite/g++.dg/warn/Wmismatched-tags-11.C
new file mode 100644
index 0000000000000000000000000000000000000000..6c4e571726aa14863728eddbc45c2915ff067a50
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wmismatched-tags-11.C
@@ -0,0 +1,23 @@
+// PR c++/106259
+// { dg-do compile }
+// { dg-options "-Wmismatched-tags" }
+
+template<typename T> struct A {
+  template<typename U>
+  struct W { };
+};
+
+template<>
+struct A<char> {
+  template<typename U>
+  class W { };
+};
+
+void
+g ()
+{
+  struct A<char>::W<int> w1; // { dg-warning "mismatched" }
+  struct A<int>::W<int> w2;
+  class A<char>::W<int> w3;
+  class A<int>::W<int> w4; // { dg-warning "mismatched" }
+}