diff --git a/crash_reporter/warn_collector.l b/crash_reporter/warn_collector.l
index d0977dcf6..7b6575bf9 100644
--- a/crash_reporter/warn_collector.l
+++ b/crash_reporter/warn_collector.l
@@ -48,7 +48,7 @@ END_TRACE       {PREFIX}" ---[ end trace".*
 
 ^{CUT_HERE}\n{WARNING}          BEGIN(PRE_WARN);
 .|\n                            /* ignore all other input in state 0 */
-<PRE_WARN>.*\n                  if (WarnStart()) {
+<PRE_WARN>[^ ]+\n               if (WarnStart()) {  /* yytext is file:line */
                                   BEGIN(WARN); ECHO;
                                 } else {
                                   BEGIN(0);