diff --git a/packages/config-loader/src/lib/secrets.ts b/packages/config-loader/src/lib/secrets.ts
index e1a7f5fd72..af651658f6 100644
--- a/packages/config-loader/src/lib/secrets.ts
+++ b/packages/config-loader/src/lib/secrets.ts
@@ -107,6 +107,9 @@ export async function readSecret(
     return ctx.env[secret.env];
   }
   if ('data' in secret) {
+    console.warn(
+      `Configuration uses deprecated $data key, use $include instead.`,
+    );
     const url =
       'path' in secret ? `${secret.data}#${secret.path}` : secret.data;
     const [filePath, dataPath] = url.split(/#(.*)/);