diff --git a/Modules/_multiprocessing/semaphore.c b/Modules/_multiprocessing/semaphore.c
index 1dfd08e..5bda1ce 100644
--- a/Modules/_multiprocessing/semaphore.c
+++ b/Modules/_multiprocessing/semaphore.c
@@ -433,7 +433,7 @@
         return NULL;
     }
 
-    PyOS_snprintf(buffer, sizeof(buffer), "/mp%d-%d", getpid(), counter++);
+    PyOS_snprintf(buffer, sizeof(buffer), "/mp%ld-%d", (long)getpid(), counter++);
 
     SEM_CLEAR_ERROR();
     handle = SEM_CREATE(buffer, value, maxvalue);