diff --git a/ChangeLog b/ChangeLog
index 132374aef1..8b028a1d44 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Dec  9 02:18:52 2015  Koichi Sasada  <ko1@atdot.net>
+
+	* compile.c (ibf_dump_memsize): should check NULL.
+
 Wed Dec  9 01:46:35 2015  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* string.c (rb_str_init): now accepts new option parameter `encoding'.
diff --git a/compile.c b/compile.c
index 83132b741c..517b500996 100644
--- a/compile.c
+++ b/compile.c
@@ -8054,11 +8054,16 @@ ibf_dump_free(void *ptr)
 static size_t
 ibf_dump_memsize(const void *ptr)
 {
-    struct ibf_dump *dump = (struct ibf_dump *)ptr;
-    size_t size = sizeof(*dump);
-    if (dump->iseq_table) size += st_memsize(dump->iseq_table);
-    if (dump->id_table) size += st_memsize(dump->id_table);
-    return size;
+    if (ptr) {
+	struct ibf_dump *dump = (struct ibf_dump *)ptr;
+	size_t size = sizeof(*dump);
+	if (dump->iseq_table) size += st_memsize(dump->iseq_table);
+	if (dump->id_table) size += st_memsize(dump->id_table);
+	return size;
+    }
+    else {
+	return 0;
+    }
 }
 
 static const rb_data_type_t ibf_dump_type = {