diff --git a/gcc/objc/ChangeLog b/gcc/objc/ChangeLog
index 636bf85de1b..47c896a7073 100644
--- a/gcc/objc/ChangeLog
+++ b/gcc/objc/ChangeLog
@@ -1,3 +1,9 @@
+2010-11-29  Nicola Pero  <nicola.pero@meta-innovation.com>
+
+	* objc-act.c (start_class): When a class is reimplemented,
+	generate an error and avoid adding the class to the list of
+	implemented classes again, but do not return error_mark_node.
+
 2010-11-29  Nicola Pero  <nicola.pero@meta-innovation.com>
 
 	* objc-act.c (objc_maybe_build_component_ref): Removed TODO.
diff --git a/gcc/objc/objc-act.c b/gcc/objc/objc-act.c
index 2382da4fd4d..8de8e255e24 100644
--- a/gcc/objc/objc-act.c
+++ b/gcc/objc/objc-act.c
@@ -9537,10 +9537,13 @@ start_class (enum tree_code code, tree class_name, tree super_name,
 	    {
 	      error ("reimplementation of class %qE",
 		     class_name);
-	      return error_mark_node;
+	      /* TODO: error message saying where it was previously
+		 implemented.  */
+	      break;
 	    }
-	implemented_classes = tree_cons (NULL_TREE, class_name,
-					 implemented_classes);
+	if (chain == NULL_TREE)
+	  implemented_classes = tree_cons (NULL_TREE, class_name,
+					   implemented_classes);
       }
 
       /* Reset for multiple classes per file.  */
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 0a154e003a5..5792e66d131 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2010-11-29  Nicola Pero  <nicola.pero@meta-innovation.com>
+
+	* objc.dg/duplicate-class-1.m: New.
+	* obj-c++.dg/duplicate-class-1.mm: New.
+
 2010-11-29  Nicola Pero  <nicola.pero@meta-innovation.com>
 
 	* objc.dg/property/dotsyntax-21.m
diff --git a/gcc/testsuite/obj-c++.dg/duplicate-class-1.mm b/gcc/testsuite/obj-c++.dg/duplicate-class-1.mm
new file mode 100644
index 00000000000..9476533d1ea
--- /dev/null
+++ b/gcc/testsuite/obj-c++.dg/duplicate-class-1.mm
@@ -0,0 +1,31 @@
+/* Contributed by Nicola Pero <nicola.pero@meta-innovation.com>, November 2010.  */
+/* { dg-do compile } */
+
+/* Test that a duplicated @implementation for the same class does not
+   crash the compiler.  */
+
+@interface Test
+{
+  Class isa;
+}
+- (int) test;
+@end
+
+@implementation Test
+- (int) test
+{
+  return 4;
+}
+@end
+
+/* The most likely cause is that the programmer meant this to be a
+   category, so check what happens if we have some different methods
+   in there.  */
+@implementation Test /* { dg-error "reimplementation of class .Test." } */
+- (int) test2
+{
+  return [self test];
+}
+@end
+/* { dg-warning "incomplete implementation" "" { target *-*-* } 29 } */
+/* { dg-warning "not found" "" { target *-*-* } 29 } */
diff --git a/gcc/testsuite/objc.dg/duplicate-class-1.m b/gcc/testsuite/objc.dg/duplicate-class-1.m
new file mode 100644
index 00000000000..f86159211b3
--- /dev/null
+++ b/gcc/testsuite/objc.dg/duplicate-class-1.m
@@ -0,0 +1,31 @@
+/* Contributed by Nicola Pero <nicola.pero@meta-innovation.com>, November 2010.  */
+/* { dg-do compile } */
+
+/* Test that a duplicated @implementation for the same class does not
+   crash the compiler.  */
+
+@interface Test
+{
+  Class isa;
+}
+- (int) test;
+@end
+
+@implementation Test
+- (int) test
+{
+  return 4;
+}
+@end
+
+/* The most likely cause is that the programmer meant this to be a
+   category, so check what happens if we have some different methods
+   in there.  */
+@implementation Test
+- (int) test2  /* { dg-error "reimplementation of class .Test." } */
+{
+  return [self test];
+}
+@end
+/* { dg-warning "incomplete implementation" "" { target *-*-* } 29 } */
+/* { dg-warning "not found" "" { target *-*-* } 29 } */