diff --git a/src/core/dhcp.c b/src/core/dhcp.c
index 7037ef77..1b1576ea 100644
--- a/src/core/dhcp.c
+++ b/src/core/dhcp.c
@@ -67,6 +67,9 @@
  * to remove the DHCP client.
  *
  */
+ 
+#include <string.h>
+ 
 #include "lwip/stats.h"
 #include "lwip/mem.h"
 #include "lwip/udp.h"
@@ -940,7 +943,7 @@ static err_t dhcp_release(struct netif *netif)
   dhcp->tries++;
   msecs = dhcp->tries < 10 ? dhcp->tries * 1000 : 10 * 1000;
   dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
-   LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | DBG_STATE, ("dhcp_release(): set request timeout %u msecs\n", msecs));
+  LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | DBG_STATE, ("dhcp_release(): set request timeout %u msecs\n", msecs));
   /* remove IP address from interface */
   netif_set_ipaddr(netif, IP_ADDR_ANY);
   netif_set_gw(netif, IP_ADDR_ANY);
diff --git a/src/core/mem.c b/src/core/mem.c
index c5214800..aea62963 100644
--- a/src/core/mem.c
+++ b/src/core/mem.c
@@ -36,6 +36,7 @@
  *
  */
 
+#include <string.h>
 
 #include "lwip/arch.h"
 #include "lwip/opt.h"
diff --git a/src/core/raw.c b/src/core/raw.c
index 9dcd8065..95f3a5a9 100644
--- a/src/core/raw.c
+++ b/src/core/raw.c
@@ -38,6 +38,8 @@
  *
  */
 
+#include <string.h>
+
 #include "lwip/opt.h"
 
 #include "lwip/def.h"
diff --git a/src/core/stats.c b/src/core/stats.c
index 02ff1a6d..56768896 100644
--- a/src/core/stats.c
+++ b/src/core/stats.c
@@ -30,6 +30,7 @@
  *
  */
 
+#include <string.h>
 
 #include "lwip/opt.h"
 
diff --git a/src/core/tcp.c b/src/core/tcp.c
index b09002f2..5ca2a8fa 100644
--- a/src/core/tcp.c
+++ b/src/core/tcp.c
@@ -41,6 +41,8 @@
  *
  */
 
+#include <string.h>
+
 #include "lwip/opt.h"
 #include "lwip/def.h"
 #include "lwip/mem.h"
diff --git a/src/core/udp.c b/src/core/udp.c
index 8011dd81..43fae895 100644
--- a/src/core/udp.c
+++ b/src/core/udp.c
@@ -42,6 +42,8 @@
  *
  */
 
+#include <string.h>
+
 #include "lwip/opt.h"
 
 #include "lwip/def.h"