diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index bb646060b49e7b037eab123cb15c2ec568a1f599..765ce9cc0b56e449afec14628f6b6747e589655a 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2005-08-22  Volker Reichelt  <reichelt@igpm.rwth-aachen.de>
+
+	PR c++/23089
+	* decl.c (require_complete_types_for_parms): Mark incomplete types
+	as invalid.
+
 2005-08-19  Volker Reichelt  <reichelt@igpm.rwth-aachen.de>
 
 	* parser.c (cp_parser_nth_token_starts_template_argument_list_p):
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index eb212c27dce885f0c2a8c558c6389bd262e36f88..9929eb6b2c24230022d9755c881ea3129259e8d5 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -8305,14 +8305,16 @@ require_complete_types_for_parms (tree parms)
     {
       if (dependent_type_p (TREE_TYPE (parms)))
 	continue;
-      if (VOID_TYPE_P (TREE_TYPE (parms)))
-	/* grokparms will have already issued an error.  */
-	TREE_TYPE (parms) = error_mark_node;
-      else if (complete_type_or_else (TREE_TYPE (parms), parms))
+      if (!VOID_TYPE_P (TREE_TYPE (parms))
+	  && complete_type_or_else (TREE_TYPE (parms), parms))
 	{
 	  relayout_decl (parms);
 	  DECL_ARG_TYPE (parms) = type_passed_as (TREE_TYPE (parms));
 	}
+      else
+	/* grokparms or complete_type_or_else will have already issued
+	   an error.  */
+	TREE_TYPE (parms) = error_mark_node;
     }
 }
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 518c6a00496ea2842282613a5941e58dcf2bb4c3..5d6a6823659fc9d8ae848e4f2c3b2201ff36df0f 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2005-08-22  Volker Reichelt  <reichelt@igpm.rwth-aachen.de>
+
+	PR c++/23089
+	* g++.dg/other/incomplete1.C: New test.
+
 2005-08-22  Ira Rosen  <irar@il.ibm.com>   
 
 	* gcc.dg/vect/vect-22.c: Add test for float. All four loops
diff --git a/gcc/testsuite/g++.dg/other/incomplete1.C b/gcc/testsuite/g++.dg/other/incomplete1.C
new file mode 100644
index 0000000000000000000000000000000000000000..cb7970fad1c22b22df3e497c872b3e94f886e219
--- /dev/null
+++ b/gcc/testsuite/g++.dg/other/incomplete1.C
@@ -0,0 +1,7 @@
+// PR c++/23089
+// Origin: Flash Sheridan  <flash@pobox.com>
+// ICE on incomplete type
+// { dg-do compile }
+// { dg-options "-O" }
+
+void foo(struct A) {} // { dg-error "incomplete type|forward declaration" }