diff --git a/src/core/tcp.c b/src/core/tcp.c
index ed8758f5..d53ce135 100644
--- a/src/core/tcp.c
+++ b/src/core/tcp.c
@@ -559,7 +559,9 @@ tcp_slowtmr(void)
   /* Steps through all of the active PCBs. */
   prev = NULL;
   pcb = tcp_active_pcbs;
-  if (pcb == NULL) LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: no active pcbs\n"));
+  if (pcb == NULL) {
+    LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: no active pcbs\n"));
+  }
   while (pcb != NULL) {
     LWIP_DEBUGF(TCP_DEBUG, ("tcp_slowtmr: processing active pcb\n"));
     LWIP_ASSERT("tcp_slowtmr: active pcb->state != CLOSED\n", pcb->state != CLOSED);