--- a/extensions/cookie/nsCookiePermission.cpp
+++ b/extensions/cookie/nsCookiePermission.cpp
@@ -114,17 +114,17 @@ nsCookiePermission::PrefChanged(nsIPrefB
       val = ACCEPT_NORMALLY;
     }
     mCookiesLifetimePolicy = val;
   }
 
   if (PREF_CHANGED(kCookiesLifetimeDays) &&
       NS_SUCCEEDED(aPrefBranch->GetIntPref(kCookiesLifetimeDays, &val)))
     // save cookie lifetime in seconds instead of days
-    mCookiesLifetimeSec = val * 24 * 60 * 60;
+    mCookiesLifetimeSec = (int64_t)val * 24 * 60 * 60;
 }
 
 NS_IMETHODIMP
 nsCookiePermission::SetAccess(nsIURI         *aURI,
                               nsCookieAccess  aAccess)
 {
   // Lazily initialize ourselves
   if (!EnsureInitialized())