diff --git a/ChangeLog b/ChangeLog
index 129d4ee6fc..27691e8641 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri May  2 18:17:37 2003  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* compar.c (cmp_gt): raises ArgumentError when "<=>" give nil.
+	  inspired by discussion on comp.lang.python.
+
 Fri May  2 17:37:01 2003  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* lib/cgi/session.rb (CGI::Session::initialize): updated to
diff --git a/compar.c b/compar.c
index 42258d59cb..0a5a10ee23 100644
--- a/compar.c
+++ b/compar.c
@@ -30,6 +30,13 @@ rb_cmpint(val)
     return 0;
 }
 
+static VALUE
+cmperr()
+{
+    rb_raise(rb_eArgError, "comparison failed");
+    return Qnil;		/* not reached */
+}
+
 static VALUE
 cmp_equal(x, y)
     VALUE x, y;
@@ -37,8 +44,9 @@ cmp_equal(x, y)
     int c;
 
     if (x == y) return Qtrue;
+
     c  = rb_funcall(x, cmp, 1, y);
-    if (NIL_P(c)) return Qfalse;
+    if (NIL_P(c)) return Qnil;
     if (c == INT2FIX(0)) return Qtrue;
     if (rb_cmpint(c) == 0) return Qtrue;
     return Qfalse;
@@ -50,7 +58,7 @@ cmp_gt(x, y)
 {
     VALUE c = rb_funcall(x, cmp, 1, y);
 
-    if (NIL_P(c)) return Qnil;
+    if (NIL_P(c)) return cmperr();
     if (rb_cmpint(c) > 0) return Qtrue;
     return Qfalse;
 }
@@ -61,7 +69,7 @@ cmp_ge(x, y)
 {
     VALUE c = rb_funcall(x, cmp, 1, y);
 
-    if (NIL_P(c)) return Qnil;
+    if (NIL_P(c)) return cmperr();
     if (rb_cmpint(c) >= 0) return Qtrue;
     return Qfalse;
 }
@@ -72,7 +80,7 @@ cmp_lt(x, y)
 {
     VALUE c = rb_funcall(x, cmp, 1, y);
 
-    if (NIL_P(c)) return Qnil;
+    if (NIL_P(c)) return cmperr();
     if (rb_cmpint(c) < 0) return Qtrue;
     return Qfalse;
 }
@@ -83,7 +91,7 @@ cmp_le(x, y)
 {
     VALUE c = rb_funcall(x, cmp, 1, y);
 
-    if (NIL_P(c)) return Qnil;
+    if (NIL_P(c)) return cmperr();
     if (rb_cmpint(c) <= 0) return Qtrue;
     return Qfalse;
 }