--- a/devtools/client/shared/test/browser_num-l10n.js
+++ b/devtools/client/shared/test/browser_num-l10n.js
@@ -17,11 +17,17 @@ function test() {
   is(l10n.numberWithDecimals(1.0001, 2), "1",
     "The third number was properly localized.");
   is(l10n.numberWithDecimals(NaN, 2), "0",
     "NaN was properly localized.");
   is(l10n.numberWithDecimals(null, 2), "0",
     "`null` was properly localized.");
   is(l10n.numberWithDecimals(undefined, 2), "0",
     "`undefined` was properly localized.");
+  is(l10n.numberWithDecimals(-1234.56789, 2), "-1,234.57",
+    "Negative number was properly localized.");
+  is(l10n.numberWithDecimals(1234.56789, 0), "1,235",
+    "Number was properly localized with decimals set 0.");
+  is(l10n.numberWithDecimals(-1234.56789, 0), "-1,235",
+    "Negative number was properly localized with decimals set 0.");
 
   finish();
 }