diff --git a/src/api/build.ts b/src/api/build.ts
index ecf5939..f2979ec 100644
--- a/src/api/build.ts
+++ b/src/api/build.ts
@@ -218,12 +218,12 @@ export async function buildToTinybird(
     );
   }
 
-  // Helper to format errors
+  // Helper to format errors - always returns a meaningful string
   const formatErrors = (): string => {
     if (body.errors && body.errors.length > 0) {
       return body.errors.map(e => {
         const prefix = e.filename ? `[${e.filename}] ` : '';
-        return `${prefix}${e.error}`;
+        return `${prefix}${e.error ?? 'Unknown error'}`;
       }).join('\n');
     }
     return body.error || `HTTP ${response.status}: ${response.statusText}`;
diff --git a/src/cli/index.ts b/src/cli/index.ts
index 368fef8..191b444 100644
--- a/src/cli/index.ts
+++ b/src/cli/index.ts
@@ -539,8 +539,9 @@ function createCli(): Command {
         // Show detailed errors if available
         if (deploy?.errors && deploy.errors.length > 0) {
           output.showBuildErrors(deploy.errors);
-        } else if (result.error) {
-          output.error(result.error);
+        } else {
+          const errorMessage = result.error ?? deploy?.error;
+          output.error(errorMessage ?? "Deploy failed (run with TINYBIRD_DEBUG=1 for more info)");
         }
         output.showDeployFailure();
         process.exit(1);
@@ -730,8 +731,9 @@ function createCli(): Command {
               const { deploy } = result;
               if (deploy?.errors && deploy.errors.length > 0) {
                 output.showBuildErrors(deploy.errors);
-              } else if (result.error) {
-                output.error(result.error);
+              } else {
+                const errorMessage = result.error ?? deploy?.error;
+                output.error(errorMessage ?? "Build failed (run with TINYBIRD_DEBUG=1 for more info)");
               }
               output.showBuildFailure(true);
               return;