--- a/toolkit/components/url-classifier/ProtocolParser.cpp
+++ b/toolkit/components/url-classifier/ProtocolParser.cpp
@@ -125,17 +125,17 @@ ProtocolParser::ProcessControl(bool* aDo
     PARSER_LOG(("Processing %s\n", line.get()));
 
     if (StringBeginsWith(line, NS_LITERAL_CSTRING("i:"))) {
       // Set the table name from the table header line.
       SetCurrentTable(Substring(line, 2));
     } else if (StringBeginsWith(line, NS_LITERAL_CSTRING("n:"))) {
       if (PR_sscanf(line.get(), "n:%d", &mUpdateWait) != 1) {
         PARSER_LOG(("Error parsing n: '%s' (%d)", line.get(), mUpdateWait));
-        mUpdateWait = 0;
+        return NS_ERROR_FAILURE;
       }
     } else if (line.EqualsLiteral("r:pleasereset")) {
       mResetRequested = true;
     } else if (StringBeginsWith(line, NS_LITERAL_CSTRING("u:"))) {
       rv = ProcessForward(line);
       NS_ENSURE_SUCCESS(rv, rv);
     } else if (StringBeginsWith(line, NS_LITERAL_CSTRING("a:")) ||
                StringBeginsWith(line, NS_LITERAL_CSTRING("s:"))) {