diff --git a/ChangeLog b/ChangeLog
index 2a86630a40..75c49e478e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Mon May 23 12:47:09 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* include/ruby/ruby.h (rb_scan_args0): raise fatal error if
+	  variable argument length does not match, it is a bug in the code
+	  which uses rb_scan_args, not a runtime error.
+
 Mon May 23 12:30:29 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* ext/bigdecimal/bigdecimal.c (GetVpValueWithPrec): consider
diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index fe2297c567..10c220d3a2 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -2203,6 +2203,12 @@ rb_scan_args0(int argc, const VALUE *argv, const char *fmt, int varc, VALUE *var
     }
     n_mand = n_lead + n_trail;
 
+    vari = n_mand + n_opt + f_var + f_hash + f_block;
+    if (vari != varc) {
+	rb_fatal("variable argument length doesn't match* %d %d", vari, varc);
+    }
+    vari = 0;
+
     if (argc < n_mand)
 	goto argc_error;
 
@@ -2282,9 +2288,6 @@ rb_scan_args0(int argc, const VALUE *argv, const char *fmt, int varc, VALUE *var
       argc_error:
 	rb_error_arity(argc, n_mand, f_var ? UNLIMITED_ARGUMENTS : n_mand + n_opt);
     }
-    if (vari != varc) {
-	rb_raise(rb_eRuntimeError, "variable argument length doesn't match* %d %d", vari, varc);
-    }
 
     return argc;
 }