diff --git a/ChangeLog b/ChangeLog
index eec1322d3c..eb8c5cae46 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Nov 25 03:26:04 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* numeric.c (num_step): treat infinite step specially.
+	  [ruby-dev:37157] fix: #781.
+
 Tue Nov 25 01:23:25 2008  Tadayoshi Funaba  <tadf@dotrb.org>
 
 	* lib/date/format.rb (strftime): ignores '_' flag for %[LN].
diff --git a/numeric.c b/numeric.c
index 042e0c306f..c2f5e60c16 100644
--- a/numeric.c
+++ b/numeric.c
@@ -1503,10 +1503,15 @@ num_step(int argc, VALUE *argv, VALUE from)
 	double err = (fabs(beg) + fabs(end) + fabs(end-beg)) / fabs(unit) * epsilon;
 	long i;
 
-	if (err>0.5) err=0.5;
-	n = floor(n + err) + 1;
-	for (i=0; i<n; i++) {
-	    rb_yield(DBL2NUM(i*unit+beg));
+	if (isinf(unit)) {
+	    if (unit > 0) rb_yield(DBL2NUM(beg));
+	}
+	else {
+	    if (err>0.5) err=0.5;
+	    n = floor(n + err) + 1;
+	    for (i=0; i<n; i++) {
+		rb_yield(DBL2NUM(i*unit+beg));
+	    }
 	}
     }
     else {