1 files changed, 12 insertions, 1 deletions
diff --git a/tools/ts_library_builder/build_library.ts b/tools/ts_library_builder/build_library.ts
index af3fb599d..e1a64215f 100644
--- a/tools/ts_library_builder/build_library.ts
+++ b/tools/ts_library_builder/build_library.ts
@@ -21,7 +21,8 @@ import {
   loadFiles,
   logDiagnostics,
   namespaceSourceFile,
-  normalizeSlashes
+  normalizeSlashes,
+  addTypeAlias
 } from "./ast_util";
 
 export interface BuildLibraryOptions {
@@ -216,6 +217,16 @@ export function mergeGlobal({
     addInterfaceProperty(interfaceDeclaration, property, type);
   }
 
+  // We need to copy over any type aliases
+  for (const typeAlias of sourceFile.getTypeAliases()) {
+    addTypeAlias(
+      targetSourceFile,
+      typeAlias.getName(),
+      typeAlias.getType().getText(sourceFile),
+      true
+    );
+  }
+
   // We need to ensure that we only namespace each source file once, so we
   // will use this map for tracking that.
   const sourceFileMap = new Map<SourceFile, string>();