diff --git a/libjava/ChangeLog b/libjava/ChangeLog
index 0d0c66b5319..e867cbfcf7b 100644
--- a/libjava/ChangeLog
+++ b/libjava/ChangeLog
@@ -1,3 +1,10 @@
+2001-09-05  Corey Minyard  <minyard@acm.org>
+	    Tom Tromey  <tromey@redhat.com>
+
+	* java/lang/natClassLoader.cc: Include VirtualMachineError.h
+	(_Jv_RegisterClassHookDefault): Throw error if a class is
+	registered twice.
+
 2001-09-05  Tom Tromey  <tromey@redhat.com>
 
 	* java/lang/natSystem.cc (init_properties): Default locale is
diff --git a/libjava/java/lang/natClassLoader.cc b/libjava/java/lang/natClassLoader.cc
index 890a4a7d879..70dea6db84a 100644
--- a/libjava/java/lang/natClassLoader.cc
+++ b/libjava/java/lang/natClassLoader.cc
@@ -33,6 +33,7 @@ details.  */
 #include <java/lang/ClassNotFoundException.h>
 #include <java/lang/ClassCircularityError.h>
 #include <java/lang/IncompatibleClassChangeError.h>
+#include <java/lang/VirtualMachineError.h>
 #include <java/lang/reflect/Modifier.h>
 #include <java/lang/Runtime.h>
 #include <java/lang/StringBuffer.h>
@@ -453,6 +454,22 @@ void
 _Jv_RegisterClassHookDefault (jclass klass)
 {
   jint hash = HASH_UTF (klass->name);
+
+  jclass check_class = loaded_classes[hash];
+
+  // If the class is already registered, don't re-register it.
+  while (check_class != NULL)
+    {
+      if (check_class == klass)
+	{
+	  // If you get this, it means you have the same class in two
+	  // different libraries.
+	  throw new java::lang::VirtualMachineError (JvNewStringLatin1 ("class registered twice"));
+	}
+
+      check_class = check_class->next;
+    }
+
   klass->next = loaded_classes[hash];
   loaded_classes[hash] = klass;
 }