diff --git a/mozilla/js/src/jsstr.c b/mozilla/js/src/jsstr.c
index b8d96fd674f..480066d6629 100644
--- a/mozilla/js/src/jsstr.c
+++ b/mozilla/js/src/jsstr.c
@@ -2825,6 +2825,9 @@ js_CompareStrings(JSString *str1, JSString *str2)
     const jschar *s1, *s2;
     intN cmp;
 
+    JS_ASSERT(str1);
+    JS_ASSERT(str2);
+
     /* Fast case: pointer equality could be a quick win. */
     if (str1 == str2)
         return 0;
@@ -2846,6 +2849,9 @@ js_EqualStrings(JSString *str1, JSString *str2)
     size_t n;
     const jschar *s1, *s2;
 
+    JS_ASSERT(str1);
+    JS_ASSERT(str2);
+
     /* Fast case: pointer equality could be a quick win. */
     if (str1 == str2)
         return JS_TRUE;