diff --git a/externs/mediakeys.js b/externs/mediakeys.js
index f763bdcaed..40f62b1410 100644
--- a/externs/mediakeys.js
+++ b/externs/mediakeys.js
@@ -28,11 +28,11 @@ var MediaKeySystemMediaCapability;
 
 
 /** @typedef {{
- *   initDataTypes: Array.<string>,
- *   audioCapabilities: Array.<!MediaKeySystemMediaCapability>,
- *   videoCapabilities: Array.<!MediaKeySystemMediaCapability>,
- *   distinctiveIdentifier: string,
- *   persistentState: string
+ *   initDataTypes: (Array.<string>|undefined),
+ *   audioCapabilities: (Array.<!MediaKeySystemMediaCapability>|undefined),
+ *   videoCapabilities: (Array.<!MediaKeySystemMediaCapability>|undefined),
+ *   distinctiveIdentifier: (string|undefined),
+ *   persistentState: (string|undefined)
  * }} */
 var MediaKeySystemConfiguration;
 
diff --git a/lib/player/player.js b/lib/player/player.js
index 4719e27b6e..c5896a317f 100644
--- a/lib/player/player.js
+++ b/lib/player/player.js
@@ -419,9 +419,9 @@ shaka.player.Player.prototype.buildKeySystemQueries_ =
     var mksc = mediaKeySystemConfigs[keySystem];
     if (!mksc) {
       mksc = mediaKeySystemConfigs[keySystem] = {
-        audioCapabilities: [],
-        videoCapabilities: [],
-        initDataTypes: [],
+        audioCapabilities: undefined,
+        videoCapabilities: undefined,
+        initDataTypes: undefined,
         distinctiveIdentifier: 'optional',
         persistentState: 'optional'
       };
@@ -433,9 +433,12 @@ shaka.player.Player.prototype.buildKeySystemQueries_ =
     if (!cfg.fullMimeType) continue;
 
     var capName = cfg.contentType + 'Capabilities';
-    if (!mksc[capName]) continue;  // not a capability we can check for!
+    if (!(capName in mksc)) continue;  // not a capability we can check for!
 
     anythingSpecified = true;
+    if (!mksc[capName]) {
+      mksc[capName] = [];
+    }
     mksc[capName].push({ contentType: cfg.fullMimeType });
   }
 
@@ -496,8 +499,9 @@ shaka.player.Player.prototype.chooseEncrypted_ =
     if (chosenStreams.has(contentType)) continue;  // not needed!
 
     var capName = contentType + 'Capabilities';
-    var caps = mksc[capName][0];
-    if (!caps) continue;  // type not found!
+    var caps = mksc[capName];
+    if (!caps || !caps.length) continue;  // type not found!
+    caps = caps[0];
 
     // Find which StreamConfigs match the selected MediaKeySystemConfiguration.
     var chosenCfgs = [];