diff --git a/Source/NSEnumerator.m b/Source/NSEnumerator.m
index cf6735b33..96ca2e365 100644
--- a/Source/NSEnumerator.m
+++ b/Source/NSEnumerator.m
@@ -97,12 +97,3 @@ - (NSUInteger) countByEnumeratingWithState: (NSFastEnumerationState*)state
 }
 @end
 
-/**
- * objc_enumerationMutation() is called whenever a collection mutates in the
- * middle of fast enumeration.
- */
-void objc_enumerationMutation(id obj)
-{
-  [NSException raise: NSGenericException 
-    format: @"Collection %@ was mutated while being enumerated", obj];
-}
diff --git a/Source/NSObject.m b/Source/NSObject.m
index eb74ca365..4ee876b9a 100644
--- a/Source/NSObject.m
+++ b/Source/NSObject.m
@@ -83,6 +83,16 @@
 #endif
 #endif
 
+/* objc_enumerationMutation() is called whenever a collection mutates in the
+ * middle of fast enumeration.  We need to have this defined and linked into
+ * any code that uses fast enumeration, so we define it in NSObject.h
+ */
+void objc_enumerationMutation(id obj)
+{
+  [NSException raise: NSGenericException 
+    format: @"Collection %@ was mutated while being enumerated", obj];
+}
+
 /* platforms which do not support weak */
 #if defined (__WIN32)
 #define WEAK_ATTRIBUTE