diff --git a/src/core/pbuf.c b/src/core/pbuf.c
index 285b1508..b95cf021 100644
--- a/src/core/pbuf.c
+++ b/src/core/pbuf.c
@@ -112,7 +112,7 @@ volatile u8_t pbuf_free_ooseq_pending;
  * can only be used with NO_SYS=0 and through tcpip_callback.
  */
 void
-pbuf_free_ooseq()
+pbuf_free_ooseq(void)
 {
   struct tcp_pcb* pcb;
   SYS_ARCH_DECL_PROTECT(old_level);
@@ -132,6 +132,7 @@ pbuf_free_ooseq()
   }
 }
 
+#if !NO_SYS
 /**
  * Just a callback function for tcpip_timeout() that calls pbuf_free_ooseq().
  */
@@ -141,18 +142,20 @@ pbuf_free_ooseq_callback(void *arg)
   LWIP_UNUSED_ARG(arg);
   pbuf_free_ooseq();
 }
+#endif /* !NO_SYS */
 
 /** Queue a call to pbuf_free_ooseq if not already queued. */
 static void
 pbuf_pool_is_empty(void)
 {
-  SYS_ARCH_DECL_PROTECT(old_level);
 #ifndef PBUF_POOL_FREE_OOSEQ_QUEUE_CALL
+  SYS_ARCH_DECL_PROTECT(old_level);
   SYS_ARCH_PROTECT(old_level);
   pbuf_free_ooseq_pending = 1;
   SYS_ARCH_UNPROTECT(old_level);
 #else /* PBUF_POOL_FREE_OOSEQ_QUEUE_CALL */
   u8_t queued;
+  SYS_ARCH_DECL_PROTECT(old_level);
   SYS_ARCH_PROTECT(old_level);
   queued = pbuf_free_ooseq_pending;
   pbuf_free_ooseq_pending = 1;