--- a/mobile/android/chrome/content/browser.js
+++ b/mobile/android/chrome/content/browser.js
@@ -6319,18 +6319,17 @@ var ViewportHandler = {
       if (defaultZoom >= 0) {
         scale = defaultZoom / 1000;
         autoSize = false;
       }
     }
 
     scale = this.clamp(scale, kViewportMinScale, kViewportMaxScale);
     minScale = this.clamp(minScale, kViewportMinScale, kViewportMaxScale);
-    maxScale = this.clamp(maxScale, minScale, kViewportMaxScale);
-
+    maxScale = this.clamp(maxScale, (isNaN(minScale) ? kViewportMinScale : minScale), kViewportMaxScale);
     if (autoSize) {
       // If initial scale is 1.0 and width is not set, assume width=device-width
       autoSize = (widthStr == "device-width" ||
                   (!widthStr && (heightStr == "device-height" || scale == 1.0)));
     }
 
     let isRTL = aWindow.document.documentElement.dir == "rtl";