diff --git a/sweet/common/gotool.go b/sweet/common/gotool.go
index 20fc76c..b86c6d0 100644
--- a/sweet/common/gotool.go
+++ b/sweet/common/gotool.go
@@ -43,6 +43,11 @@
 	}
 	// Use cmd.Output to get an ExitError with Stderr populated.
 	_, err := cmd.Output()
+	if ee, ok := err.(*exec.ExitError); ok {
+		// ExitError includes stderr, but doesn't inclue it in Error.
+		// Create a new error that does display stderr.
+		return fmt.Errorf("%w. stderr:\n%s", err, ee.Stderr)
+	}
 	return err
 }