diff --git a/lib/util/stream_utils.js b/lib/util/stream_utils.js
index 9cdc80f06a..13d2ae12f1 100644
--- a/lib/util/stream_utils.js
+++ b/lib/util/stream_utils.js
@@ -501,6 +501,40 @@ shaka.util.StreamUtils = class {
   }
 
 
+  /**
+   * Constructs a string out of an object, similar to the JSON.stringify method.
+   * Unlike that method, this guarantees that the order of the keys is
+   * alphabetical, so it can be used as a way to reliably compare two objects.
+   *
+   * @param {!Object} obj
+   * @return {string}
+   * @private
+   */
+  static alphabeticalKeyOrderStringify_(obj) {
+    const keys = [];
+    for (const key in obj) {
+      keys.push(key);
+    }
+    // Alphabetically sort the keys, so they will be in a reliable order.
+    keys.sort();
+
+    const terms = [];
+    for (const key of keys) {
+      const escapedKey = JSON.stringify(key);
+      const value = obj[key];
+      if (value instanceof Object) {
+        const stringifiedValue =
+            shaka.util.StreamUtils.alphabeticalKeyOrderStringify_(value);
+        terms.push(escapedKey + ':' + stringifiedValue);
+      } else {
+        const escapedValue = JSON.stringify(value);
+        terms.push(escapedKey + ':' + escapedValue);
+      }
+    }
+    return '{' + terms.join(',') + '}';
+  }
+
+
   /**
    * Queries mediaCapabilities for the decoding info for that decoding config,
    * and assigns it to the given variant.
@@ -510,10 +544,14 @@ shaka.util.StreamUtils = class {
    * @private
    */
   static async getDecodingInfosForVariant_(variant, decodingConfig) {
+    const cacheKey =
+        shaka.util.StreamUtils.alphabeticalKeyOrderStringify_(decodingConfig);
+
     try {
-      const cacheKey = JSON.stringify(decodingConfig);
-      const cache = shaka.util.StreamUtils.decodingConfigCache;
+      const cache = shaka.util.StreamUtils.decodingConfigCache_;
       if (cache[cacheKey]) {
+        shaka.log.v2('Using cached results of mediaCapabilities.decodingInfo',
+            'for key', cacheKey);
         variant.decodingInfos.push(cache[cacheKey]);
       } else {
         const result =
@@ -1601,9 +1639,9 @@ shaka.util.StreamUtils = class {
  * (stringified) decodingConfig.
  *
  * @type {Object.<(!string), (!MediaCapabilitiesDecodingInfo)>}
- * @export
+ * @private
  */
-shaka.util.StreamUtils.decodingConfigCache = {};
+shaka.util.StreamUtils.decodingConfigCache_ = {};
 
 
 /** @private {number} */
diff --git a/test/test/boot.js b/test/test/boot.js
index 6df7f23fce..4eb53b92e0 100644
--- a/test/test/boot.js
+++ b/test/test/boot.js
@@ -332,8 +332,8 @@ function configureJasmineEnvironment() {
   }
 
   // Reset decoding config cache after each test.
-  afterEach(() => {
-    shaka.util.StreamUtils.decodingConfigCache = {};
+  afterEach(/** @suppress {accessControls} */ () => {
+    shaka.util.StreamUtils.decodingConfigCache_ = {};
   });
 
   // Code in karma-jasmine's adapter will malform test failures when the