diff --git a/proto/caosdb/entity/v1alpha1/main.proto b/proto/caosdb/entity/v1alpha1/main.proto
index 8fb40158e7dda29df66520f65e7f3d8ad9bd3b8a..198070737b107c7ee086377bc9dc8f5919b20f2b 100644
--- a/proto/caosdb/entity/v1alpha1/main.proto
+++ b/proto/caosdb/entity/v1alpha1/main.proto
@@ -29,7 +29,7 @@ package caosdb.entity.v1alpha1;
 // errors.
 message Message {
   // The code is a machine-readable identifier.
-  string code = 1;
+  uint32 code = 1;
   // A short description of the message which is indented for human readers.
   string description = 2;
 }