diff --git a/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaServerSideAdInsertionMediaSource.java b/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaServerSideAdInsertionMediaSource.java
index 6a503d416a..9df38e116c 100644
--- a/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaServerSideAdInsertionMediaSource.java
+++ b/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaServerSideAdInsertionMediaSource.java
@@ -377,6 +377,7 @@ public final class ImaServerSideAdInsertionMediaSource extends CompositeMediaSou
 
   @Override
   public void prepareSourceInternal(@Nullable TransferListener mediaTransferListener) {
+    mainHandler.post(() -> assertSingleInstanceInPlaylist(checkNotNull(player)));
     super.prepareSourceInternal(mediaTransferListener);
     if (loader == null) {
       Loader loader = new Loader("ImaServerSideAdInsertionMediaSource");
@@ -1150,4 +1151,20 @@ public final class ImaServerSideAdInsertionMediaSource extends CompositeMediaSou
               overlayInfo.reasonDetail != null ? overlayInfo.reasonDetail : "Unknown reason"));
     }
   }
+
+  private static void assertSingleInstanceInPlaylist(Player player) {
+    int counter = 0;
+    for (int i = 0; i < player.getMediaItemCount(); i++) {
+      MediaItem mediaItem = player.getMediaItemAt(i);
+      if (mediaItem.localConfiguration != null
+          && C.SSAI_SCHEME.equals(mediaItem.localConfiguration.uri.getScheme())
+          && ImaServerSideAdInsertionUriBuilder.IMA_AUTHORITY.equals(
+              mediaItem.localConfiguration.uri.getAuthority())) {
+        if (++counter > 1) {
+          throw new IllegalStateException(
+              "Multiple IMA server side ad insertion sources not supported.");
+        }
+      }
+    }
+  }
 }
diff --git a/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaServerSideAdInsertionUriBuilder.java b/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaServerSideAdInsertionUriBuilder.java
index 8641d843b8..1334a488a2 100644
--- a/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaServerSideAdInsertionUriBuilder.java
+++ b/extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaServerSideAdInsertionUriBuilder.java
@@ -41,7 +41,7 @@ public final class ImaServerSideAdInsertionUriBuilder {
   /** The default timeout for loading the video URI, in milliseconds. */
   public static final int DEFAULT_LOAD_VIDEO_TIMEOUT_MS = 10_000;
 
-  private static final String IMA_AUTHORITY = "dai.google.com";
+  /* package */ static final String IMA_AUTHORITY = "dai.google.com";
   private static final String ADS_ID = "adsId";
   private static final String ASSET_KEY = "assetKey";
   private static final String API_KEY = "apiKey";