diff --git a/ChangeLog b/ChangeLog
index c26c6cf8b2..dffda865c0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Dec 27 21:08:23 2012  Charlie Somerville  <charlie@charliesomerville.com>
+
+	* vm_core.h (VM_DEFINECLASS_TYPE): explicit cast to enum type to avoid 64->32
+	  shorten warning
+
 Thu Dec 27 20:11:29 2012  Masaki Matsushita  <glass.saga@gmail.com>
 
 	* ext/stringio/stringio.c (strio_ungetc): raise IOError instead of RuntimeError
diff --git a/vm_core.h b/vm_core.h
index 8a4dd239a1..6ecbd70289 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -620,7 +620,7 @@ typedef enum {
     VM_DEFINECLASS_TYPE_MASK            = 0x07,
 } rb_vm_defineclass_type_t;
 
-#define VM_DEFINECLASS_TYPE(x) ((x) & VM_DEFINECLASS_TYPE_MASK)
+#define VM_DEFINECLASS_TYPE(x) ((rb_vm_defineclass_type_t)(x) & VM_DEFINECLASS_TYPE_MASK)
 #define VM_DEFINECLASS_FLAG_SCOPED         0x08
 #define VM_DEFINECLASS_FLAG_HAS_SUPERCLASS 0x10
 #define VM_DEFINECLASS_SCOPED_P(x) ((x) & VM_DEFINECLASS_FLAG_SCOPED)