diff --git a/src/WebComponents/build-lite.json b/src/WebComponents/build-lite.json
index e2e275fd8..0f1f6fd3f 100644
--- a/src/WebComponents/build-lite.json
+++ b/src/WebComponents/build-lite.json
@@ -1,5 +1,6 @@
 [
   "build/boot.js",
+  "../WeakMap/WeakMap.js",
   "../URL/URL.js",
   "../MutationObserver/MutationObserver.js",
   "../HTMLImports/build.json",
diff --git a/src/WebComponents/build.json b/src/WebComponents/build.json
index 89ea0da60..02ecfcb82 100644
--- a/src/WebComponents/build.json
+++ b/src/WebComponents/build.json
@@ -1,5 +1,6 @@
 [
   "build/boot.js",
+  "../WeakMap/WeakMap.js",
   "build/if-poly.js",
   "../ShadowDOM/build.json",
   "../ShadowCSS/ShadowCSS.js",