diff --git a/tests/test_proxy_steerable.cpp b/tests/test_proxy_steerable.cpp
index 180aacc4b7..37837b0ffd 100644
--- a/tests/test_proxy_steerable.cpp
+++ b/tests/test_proxy_steerable.cpp
@@ -5,6 +5,7 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <inttypes.h>
 
 #define CONTENT_SIZE 13
 #define CONTENT_SIZE_MAX 32
@@ -360,7 +361,7 @@ uint64_t statistics (void *proxy_control, const char *runctx)
                         zmq_atomic_counter_value (g_clients_pkts_out),
                         zmq_atomic_counter_value (g_workers_pkts_out));
             }
-            printf ("%lu ", val);
+            printf ("%" PRIu64, val);
             if (count == 7) {
                 printf ("}\n");
             }