diff --git a/demo/custom.js b/demo/custom.js
index a7a8028170..bee8a9c51b 100644
--- a/demo/custom.js
+++ b/demo/custom.js
@@ -46,6 +46,9 @@ shakaDemo.Custom = class {
     /** @private {!Set.<!ShakaDemoAssetInfo>} */
     this.assets_ = this.loadAssetInfos_();
 
+    /** @private {!HTMLInputElement} */
+    this.manifestField_;
+
     /** @private {!Array.<!shakaDemo.AssetCard>} */
     this.assetCards_ = [];
     this.savedList_ = document.createElement('div');
@@ -238,6 +241,7 @@ shakaDemo.Custom = class {
     return headersDiv;
   }
 
+
   /**
    * @param {!ShakaDemoAssetInfo} assetInProgress
    * @param {!Array.<!HTMLInputElement>} inputsToCheck
@@ -270,9 +274,14 @@ shakaDemo.Custom = class {
       if (assetInProgress.imaContentSrcId) {
         input.value = assetInProgress.imaContentSrcId;
       }
+
+      this.manifestField_.required =
+        this.checkManifestRequired_(assetInProgress);
     };
     const contentSrcIdOnChange = (input) => {
       assetInProgress.imaContentSrcId = input.value;
+      this.manifestField_.required =
+        this.checkManifestRequired_(assetInProgress);
     };
     const contentSrcIdName = shakaDemoMain.getLocalizedString(
         shakaDemo.MessageIds.IMA_CONTENT_SRC_ID);
@@ -284,9 +293,14 @@ shakaDemo.Custom = class {
       if (assetInProgress.imaVideoId) {
         input.value = assetInProgress.imaVideoId;
       }
+
+      this.manifestField_.required =
+        this.checkManifestRequired_(assetInProgress);
     };
     const videoIdOnChange = (input) => {
       assetInProgress.imaVideoId = input.value;
+      this.manifestField_.required =
+        this.checkManifestRequired_(assetInProgress);
     };
     const videoIdName = shakaDemoMain.getLocalizedString(
         shakaDemo.MessageIds.IMA_VIDEO_ID);
@@ -298,9 +312,14 @@ shakaDemo.Custom = class {
       if (assetInProgress.imaAssetKey) {
         input.value = assetInProgress.imaAssetKey;
       }
+
+      this.manifestField_.required =
+        this.checkManifestRequired_(assetInProgress);
     };
     const assetKeyChange = (input) => {
       assetInProgress.imaAssetKey = input.value;
+      this.manifestField_.required =
+        this.checkManifestRequired_(assetInProgress);
     };
     const assetKeyName = shakaDemoMain.getLocalizedString(
         shakaDemo.MessageIds.IMA_ASSET_KEY);
@@ -431,8 +450,9 @@ shakaDemo.Custom = class {
       container.appendChild(error);
 
       // Add a regex that will detect empty strings.
-      input.required = true;
+      input.required = this.checkManifestRequired_(assetInProgress);
       input.pattern = '^(?!([\r\n\t\f\v ]+)$).*$';
+      this.manifestField_ = input;
     };
     const manifestOnChange = (input) => {
       assetInProgress.manifestUri = input.value;
@@ -511,6 +531,18 @@ shakaDemo.Custom = class {
     return mainDiv;
   }
 
+  /**
+   * @param {!ShakaDemoAssetInfo} assetInProgress
+   * @private
+   */
+  checkManifestRequired_(assetInProgress) {
+    // The manifest field is required unless we're getting the manifest
+    // from the Google Ad Manager using IMA ids.
+    const isDaiAdManifest = (assetInProgress.imaContentSrcId &&
+        assetInProgress.imaVideoId) || assetInProgress.imaAssetKey != null;
+    return !isDaiAdManifest;
+  }
+
   /**
    * @param {!ShakaDemoAssetInfo} assetInProgress
    * @param {!Array.<!HTMLInputElement>} inputsToCheck
diff --git a/demo/locales/en.json b/demo/locales/en.json
index a614acaa13..4d1f37b525 100644
--- a/demo/locales/en.json
+++ b/demo/locales/en.json
@@ -115,7 +115,7 @@
   "DEMO_MANIFEST_SEARCH": "Manifest",
   "DEMO_MANIFEST_SECTION_HEADER": "Manifest",
   "DEMO_MANIFEST_URL": "Manifest URL",
-  "DEMO_MANIFEST_URL_ERROR": "Must have a manifest URL.",
+  "DEMO_MANIFEST_URL_ERROR": "Must have a manifest URL, or IMA DAI id fields",
   "DEMO_MAX_ATTEMPTS": "Max Attempts",
   "DEMO_MAX_BANDWIDTH": "Max Bandwidth",
   "DEMO_MAX_FRAMERATE": "Max Framerate",
diff --git a/demo/locales/source.json b/demo/locales/source.json
index b391be0666..fee2ca416d 100644
--- a/demo/locales/source.json
+++ b/demo/locales/source.json
@@ -464,8 +464,8 @@
     "message": "Manifest URL"
   },
   "DEMO_MANIFEST_URL_ERROR": {
-    "description": "An error that is displayed if the user does not provide a manifest URL for a custom asset.",
-    "message": "Must have a manifest URL."
+    "description": "An error that is displayed if the user does not provide a manifest URL for a custom asset or identification fields in the Google Ad Manager system.",
+    "message": "Must have a manifest URL, or IMA DAI id fields."
   },
   "DEMO_MAX_ATTEMPTS": {
     "description": "The name of a configuration value.",