diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 537d1aa5473..8893880b2c2 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,5 +1,7 @@
 2012-01-11  Jason Merrill  <jason@redhat.com>
 
+	* decl.c (decls_match): Assert that the arguments are decls.
+
 	PR c++/51613
 	* pt.c (resolve_overloaded_unification): Compare types with
 	same_type_p, not decls_match.
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index 7daac5feff4..ef43dbf86ee 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -952,6 +952,8 @@ decls_match (tree newdecl, tree olddecl)
        interested in their types.  */
     return 0;
 
+  gcc_assert (DECL_P (newdecl));
+
   if (TREE_CODE (newdecl) == FUNCTION_DECL)
     {
       tree f1 = TREE_TYPE (newdecl);