diff --git a/upb/def.c b/upb/def.c
index 1add146824..c745ff9f77 100644
--- a/upb/def.c
+++ b/upb/def.c
@@ -2339,8 +2339,7 @@ static void create_fielddef(
   }
 
   if (google_protobuf_FieldDescriptorProto_has_oneof_index(field_proto)) {
-    int oneof_index =
-        google_protobuf_FieldDescriptorProto_oneof_index(field_proto);
+    uint32_t oneof_index = google_protobuf_FieldDescriptorProto_oneof_index(field_proto);
     upb_OneofDef* oneof;
     upb_value v = upb_value_constptr(f);