diff --git a/Source/NSConcreteHashTable.m b/Source/NSConcreteHashTable.m
index e65750bf5..923df209e 100644
--- a/Source/NSConcreteHashTable.m
+++ b/Source/NSConcreteHashTable.m
@@ -302,6 +302,7 @@ NSCreateHashTableWithZone(
   if (concreteClass == Nil)
     {
       [NSConcreteHashTable class];	// Force +initialize
+      NSCAssert(concreteClass != Nil, NSInternalInconsistencyException);
     }
   table = (GSIMapTable)[concreteClass allocWithZone: zone];
 
diff --git a/Source/NSConcreteMapTable.m b/Source/NSConcreteMapTable.m
index 4625ee3b8..f5e019d58 100644
--- a/Source/NSConcreteMapTable.m
+++ b/Source/NSConcreteMapTable.m
@@ -440,6 +440,7 @@ NSCreateMapTableWithZone(
   if (concreteClass == Nil)
     {
       [NSConcreteMapTable class];	// Force +initialize
+      NSCAssert(concreteClass != Nil, NSInternalInconsistencyException);
     }
   table = (GSIMapTable)[concreteClass allocWithZone: zone];
 
@@ -1133,7 +1134,7 @@ const NSMapTableValueCallBacks NSOwnedPointerMapValueCallBacks =
 
 + (void) initialize
 {
-  if (concreteClass == 0)
+  if (concreteClass == Nil)
     {
       concreteClass = [NSConcreteMapTable class];
     }