diff --git a/ChangeLog b/ChangeLog
index 8982f9883e..581d1d337e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Thu Feb 23 19:56:48 2012  Tanaka Akira  <akr@fsij.org>
+
+	* signal.c (sig_trap): show signal name on error.
+
 Thu Feb 23 12:21:48 2012  Tanaka Akira  <akr@fsij.org>
 
 	* ext/dbm/extconf.rb: use DBM_SUFFIX only to detect header of
diff --git a/signal.c b/signal.c
index 5e475bf9d3..08ce482ded 100644
--- a/signal.c
+++ b/signal.c
@@ -937,7 +937,11 @@ sig_trap(int argc, VALUE *argv)
 
     arg.sig = trap_signm(argv[0]);
     if (reserved_signal_p(arg.sig)) {
-	rb_raise(rb_eArgError, "can't trap reserved signal");
+        const char *name = signo2signm(arg.sig);
+        if (name)
+            rb_raise(rb_eArgError, "can't trap reserved signal: SIG%s", name);
+        else
+            rb_raise(rb_eArgError, "can't trap reserved signal: %d", (int)arg.sig);
     }
 
     if (argc == 1) {