--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -3110,17 +3110,17 @@ XRE_main(int argc, char* argv[], const n
     nsCAutoString desktopStartupID;
     if (desktopStartupIDEnv) {
       desktopStartupID.Assign(desktopStartupIDEnv);
     }
 #endif
 
 #if defined(MOZ_WIDGET_QT)
     const char* qgraphicssystemARG = NULL;
-    ar = CheckArg("graphicssystem", PR_TRUE, &qgraphicssystemARG);
+    ar = CheckArg("graphicssystem", PR_TRUE, &qgraphicssystemARG, PR_FALSE);
     if (ar == ARG_FOUND)
       PR_SetEnv(PR_smprintf("MOZ_QT_GRAPHICSSYSTEM=%s", qgraphicssystemARG));
     QApplication app(gArgc, gArgv);
 #endif
 #if defined(MOZ_WIDGET_GTK2)
 #ifdef MOZ_MEMORY
     // Disable the slice allocator, since jemalloc already uses similar layout
     // algorithms, and using a sub-allocator tends to increase fragmentation.