diff --git a/packages/aws-cdk/bin/cdk.ts b/packages/aws-cdk/bin/cdk.ts
index 256a5d3bc6b61..72fda53711b99 100644
--- a/packages/aws-cdk/bin/cdk.ts
+++ b/packages/aws-cdk/bin/cdk.ts
@@ -465,7 +465,7 @@ async function initCommandLine() {
         const outfile = await exec();
         debug('outfile:', outfile);
         if (!(await fs.pathExists(outfile))) {
-          throw new Error(`Unable to find output file ${outfile}`);
+          throw new Error(`Unable to find output file ${outfile}; are you calling app.run()?`);
         }
 
         const response = await fs.readJson(outfile);