diff --git a/ChangeLog b/ChangeLog
index 623ba10a15..d3c34ffe9a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Nov 18 11:57:32 2009  TAKANO Mitsuhiro (takano32)  <tak@no32.tk>
+
+	* math.c (math_gamma): fix incorrect comparison expression.
+	  see also [ruby-dev:39709] [Bug #2381]
+
 Wed Nov 18 11:37:05 2009  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* io.c (rb_scan_open_args): move path encoding conversion
diff --git a/math.c b/math.c
index 2b877ec64e..1a448b8713 100644
--- a/math.c
+++ b/math.c
@@ -666,14 +666,13 @@ math_gamma(VALUE obj, VALUE x)
     };
     double d0, d;
     double intpart, fracpart;
-    int n;
     Need_Float(x);
     d0 = RFLOAT_VALUE(x);
     fracpart = modf(d0, &intpart);
     if (fracpart == 0.0 &&
-	0 < intpart &&
-	(n = (int)intpart - 1) < numberof(fact_table)) {
-        return DBL2NUM(fact_table[n]);
+        0 < intpart &&
+        intpart - 1 < (double)numberof(fact_table)) {
+        return DBL2NUM(fact_table[(int)intpart - 1]);
     }
     errno = 0;
     d = tgamma(d0);