--- a/testing/mochitest/tests/SimpleTest/MemoryStats.js
+++ b/testing/mochitest/tests/SimpleTest/MemoryStats.js
@@ -99,24 +99,24 @@ MemoryStats.dump = function (testNumber,
         var md = MemoryStats._getService("@mozilla.org/memory-info-dumper;1",
                                          "nsIMemoryInfoDumper");
         md.dumpMemoryReportsToNamedFile(dumpfile, function () {
             info("TEST-INFO | " + testURL + " | MEMDUMP-END");
         }, null, /* anonymize = */ false);
     }
 
     // This is the old, deprecated function.
-    if (dumpDMD && typeof(DMDReportAndDump) != undefined) {
+    if (dumpDMD && typeof(DMDReportAndDump) != "undefined") {
         var basename = "dmd-" + testNumber + "-deprecated.txt";
         var dumpfile = MemoryStats.constructPathname(dumpOutputDirectory,
                                                      basename);
         info(testURL + " | DMD-DUMP-deprecated " + dumpfile);
         DMDReportAndDump(dumpfile);
     }
 
-    if (dumpDMD && typeof(DMDAnalyzeReports) != undefined) {
+    if (dumpDMD && typeof(DMDAnalyzeReports) != "undefined") {
         var basename = "dmd-" + testNumber + ".txt";
         var dumpfile = MemoryStats.constructPathname(dumpOutputDirectory,
                                                      basename);
         info(testURL + " | DMD-DUMP " + dumpfile);
         DMDAnalyzeReports(dumpfile);
     }
 };