diff --git a/ChangeLog b/ChangeLog
index f7c5334e80..4eef45eb8e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Sep  2 13:47:30 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* math.c (domain_check): simplified.
+
 Wed Sep  2 11:32:24 2009  Koichi Sasada  <ko1@atdot.net>
 
 	* gc.c (obj_free): fix to free method table (fix memory leak).
diff --git a/math.c b/math.c
index 2734280b32..5ce16e805e 100644
--- a/math.c
+++ b/math.c
@@ -25,21 +25,18 @@ extern VALUE rb_to_float(VALUE val);
 static void
 domain_check(double x, double y, const char *msg)
 {
-    while(1) {
-	if (errno) {
-	    rb_sys_fail(msg);
-	}
-	if (isnan(y)) {
-	    if (isnan(x)) break;
+    if (!isnan(y)) return;
+    else if (isnan(x)) return;
+    else {
+	if (!errno) {
 #if defined(EDOM)
 	    errno = EDOM;
-#elif defined(ERANGE)
+#else
 	    errno = ERANGE;
 #endif
-	    continue;
 	}
-	break;
     }
+    rb_sys_fail(msg);
 }
 
 static void