diff --git a/lib/build/bundled-source.js b/lib/build/bundled-source.js
index 14ff2f8ca..d9b5a6a73 100644
--- a/lib/build/bundled-source.js
+++ b/lib/build/bundled-source.js
@@ -91,7 +91,11 @@ exports.BundledSource = class {
     this.file = file;
     this._contents = null;
     this.requiresTransform = true;
-    this.includedIn.requiresBuild = true;
+    if (this.includedIn) {
+      this.includedIn.requiresBuild = true;
+    } else {
+      logger.warn(this.path + ' is not captured by any bundle file. You might need to adjust the bundles source matcher in aurelia.json.');
+    }
   }
 
   transform() {
diff --git a/lib/build/bundler.js b/lib/build/bundler.js
index ef021f159..8969a5d9c 100644
--- a/lib/build/bundler.js
+++ b/lib/build/bundler.js
@@ -335,6 +335,7 @@ function subsume(bundles, item) {
       return;
     }
   }
+  logger.warn(item.path + ' is not captured by any bundle file. You might need to adjust the bundles source matcher in aurelia.json.');
 }
 
 function normalizeKey(p) {