diff --git a/ChangeLog b/ChangeLog
index e91eab7807..f95f231bc2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Aug 12 21:15:27 2015  Eric Wong  <e@80x24.org>
+
+	* vm_core.h (rb_call_info_kw_arg_bytes): extract from compile.c
+	* compile.c (iseq_build_callinfo_from_hash): use above function
+
 Wed Aug 12 18:00:17 2015  Koichi Sasada  <ko1@atdot.net>
 
 	* class.c (move_refined_method): same as the last commit.
diff --git a/compile.c b/compile.c
index 637f56ffff..26ee3b24fa 100644
--- a/compile.c
+++ b/compile.c
@@ -5917,7 +5917,7 @@ iseq_build_callinfo_from_hash(rb_iseq_t *iseq, VALUE op)
 	if (!NIL_P(vkw_arg)) {
 	    int i;
 	    int len = RARRAY_LENINT(vkw_arg);
-	    size_t n = sizeof(rb_call_info_kw_arg_t) + sizeof(VALUE) * (len - 1);
+	    size_t n = rb_call_info_kw_arg_bytes(len);
 
 	    kw_arg = xmalloc(n);
 	    kw_arg->keyword_len = len;
diff --git a/vm_core.h b/vm_core.h
index a032daa2ad..67458372c0 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -180,6 +180,12 @@ typedef struct rb_call_info_kw_arg_struct {
     VALUE keywords[1];
 } rb_call_info_kw_arg_t;
 
+static inline size_t
+rb_call_info_kw_arg_bytes(int keyword_len)
+{
+    return sizeof(rb_call_info_kw_arg_t) + sizeof(VALUE) * (keyword_len - 1);
+}
+
 enum method_missing_reason {
     MISSING_NOENTRY   = 0x00,
     MISSING_PRIVATE   = 0x01,