--- a/hotspot/src/os/posix/vm/os_posix.cpp	Wed Dec 09 21:24:57 2015 +0900
+++ b/hotspot/src/os/posix/vm/os_posix.cpp	Thu Dec 10 08:50:36 2015 +0100
@@ -736,12 +736,12 @@
 }
 
 // Returns:
-// "invalid (<num>)" for an invalid signal number
+// NULL for an invalid signal number
 // "SIG<num>" for a valid but unknown signal number
 // signal name otherwise.
 const char* os::exception_name(int sig, char* buf, size_t size) {
   if (!os::Posix::is_valid_signal(sig)) {
-    jio_snprintf(buf, size, "invalid (%d)", sig);
+    return NULL;
   }
   const char* const name = os::Posix::get_signal_name(sig, buf, size);
   if (strcmp(name, "UNKNOWN") == 0) {