diff --git a/ChangeLog b/ChangeLog
index 9ccb53ae0a..a34c2cb777 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Fri Oct 30 06:43:50 2015  Koichi Sasada  <ko1@atdot.net>
+
+	* vm_insnhelper.c (vm_env_cref): make it inline for performance.
+
+	* vm_insnhelper.c (rb_vm_get_cref): use NULL instead of 0.
+
 Fri Oct 30 06:20:40 2015  Koichi Sasada  <ko1@atdot.net>
 
 	* insns.def: nobody set ic->ic_value.value to Qundef.
diff --git a/vm_insnhelper.c b/vm_insnhelper.c
index 7fbdcd9c27..6a7bba92d4 100644
--- a/vm_insnhelper.c
+++ b/vm_insnhelper.c
@@ -448,7 +448,7 @@ check_cref(VALUE obj, int can_be_svar)
     }
 }
 
-static rb_cref_t *
+static inline rb_cref_t *
 vm_env_cref(const VALUE *ep)
 {
     rb_cref_t *cref;
@@ -492,11 +492,12 @@ rb_vm_get_cref(const VALUE *ep)
 {
     rb_cref_t *cref = vm_env_cref(ep);
 
-    if (cref == 0) {
+    if (cref != NULL) {
+	return cref;
+    }
+    else {
 	rb_bug("rb_vm_get_cref: unreachable");
     }
-
-    return cref;
 }
 
 void