diff --git a/server/core/CMakeLists.txt b/server/core/CMakeLists.txt
index 6c2c3579d..3d7666ff5 100644
--- a/server/core/CMakeLists.txt
+++ b/server/core/CMakeLists.txt
@@ -41,7 +41,7 @@ add_library(maxscale-common SHARED
   thread.cc
   users.cc
   utils.cc
-  worker.c
+  worker.cc
   )
 
 if(WITH_JEMALLOC)
diff --git a/server/core/worker.c b/server/core/worker.cc
similarity index 99%
rename from server/core/worker.c
rename to server/core/worker.cc
index c2778537d..f85753328 100644
--- a/server/core/worker.c
+++ b/server/core/worker.cc
@@ -51,7 +51,7 @@ static thread_local struct this_thread
  */
 typedef struct worker_message
 {
-    int      id;   /*< Message id. */
+    uint32_t id;   /*< Message id. */
     intptr_t arg1; /*< Message specific first argument. */
     intptr_t arg2; /*< Message specific second argument. */
 } WORKER_MESSAGE;