diff --git a/lib/polyfill/media_capabilities.js b/lib/polyfill/media_capabilities.js
index 1dfde7ca3d..a72283662e 100644
--- a/lib/polyfill/media_capabilities.js
+++ b/lib/polyfill/media_capabilities.js
@@ -37,7 +37,9 @@ shaka.polyfill.MediaCapabilities = class {
       return;
     }
 
-    navigator.mediaCapabilities = /** @type {!MediaCapabilities} */ ({});
+    if (!navigator.mediaCapabilities) {
+      navigator.mediaCapabilities = /** @type {!MediaCapabilities} */ ({});
+    }
     navigator.mediaCapabilities.decodingInfo =
         shaka.polyfill.MediaCapabilities.decodingInfo_;
   }