diff --git a/sys/net/application_layer/gcoap/gcoap.c b/sys/net/application_layer/gcoap/gcoap.c
index 521e0ac3a4c1f9e4da7966187b924cb1c6e347b7..d39202a58085cc8c0dbeac283ba1132db52d9233 100644
--- a/sys/net/application_layer/gcoap/gcoap.c
+++ b/sys/net/application_layer/gcoap/gcoap.c
@@ -21,6 +21,7 @@
 #include <errno.h>
 #include <stdint.h>
 #include <stdatomic.h>
+#include <string.h>
 
 #include "assert.h"
 #include "net/gcoap.h"
diff --git a/sys/net/gnrc/netif/gnrc_netif.c b/sys/net/gnrc/netif/gnrc_netif.c
index 5ec6145ea8808ed40fc6bc98f9b190309bce6753..61a5cf570bb9da74d64d8cf31f3fc58752696d1a 100644
--- a/sys/net/gnrc/netif/gnrc_netif.c
+++ b/sys/net/gnrc/netif/gnrc_netif.c
@@ -15,6 +15,8 @@
  * @author  Oliver Hahm <oliver.hahm@inria.fr>
  */
 
+#include <string.h>
+
 #include "bitfield.h"
 #include "net/ethernet.h"
 #include "net/ipv6.h"
diff --git a/sys/net/gnrc/netif/gnrc_netif_ethernet.c b/sys/net/gnrc/netif/gnrc_netif_ethernet.c
index 7aafc78808346bd52b92159b1981791e58e37caf..2ba016ddfca8d557fa63d0dfaa017cf945ef7edf 100644
--- a/sys/net/gnrc/netif/gnrc_netif_ethernet.c
+++ b/sys/net/gnrc/netif/gnrc_netif_ethernet.c
@@ -15,6 +15,8 @@
  * @author  Kaspar Schleiser <kaspar@schleiser.de>
  */
 
+#include <string.h>
+
 #ifdef MODULE_NETDEV_ETH
 #include "net/ethernet/hdr.h"
 #include "net/gnrc.h"
diff --git a/sys/net/gnrc/network_layer/ipv6/nib/_nib-internal.h b/sys/net/gnrc/network_layer/ipv6/nib/_nib-internal.h
index 78b6d1a88d776f6d4a39b9b21f1242fc1c878651..145de403f2ede688bd6dfc269fe1c0b35eecfaac 100644
--- a/sys/net/gnrc/network_layer/ipv6/nib/_nib-internal.h
+++ b/sys/net/gnrc/network_layer/ipv6/nib/_nib-internal.h
@@ -22,6 +22,7 @@
 #include <assert.h>
 #include <stdbool.h>
 #include <stdint.h>
+#include <string.h>
 
 #include "bitfield.h"
 #include "evtimer_msg.h"
diff --git a/sys/net/gnrc/network_layer/ndp/gnrc_ndp.c b/sys/net/gnrc/network_layer/ndp/gnrc_ndp.c
index e467ea9506e1542022caeccd238d99b9d1aa22ab..1d3fe847a5f2821857a2313d4ca30655d814c5c3 100644
--- a/sys/net/gnrc/network_layer/ndp/gnrc_ndp.c
+++ b/sys/net/gnrc/network_layer/ndp/gnrc_ndp.c
@@ -13,6 +13,8 @@
  * @author  Martine Lenders <m.lenders@fu-berlin.de>
  */
 
+#include <string.h>
+
 #include "net/gnrc/icmpv6.h"
 #include "net/gnrc/ipv6.h"
 #include "net/gnrc/netif/internal.h"
diff --git a/sys/net/gnrc/network_layer/sixlowpan/nd/gnrc_sixlowpan_nd.c b/sys/net/gnrc/network_layer/sixlowpan/nd/gnrc_sixlowpan_nd.c
index 7a6eb118a36307e23233fcde92f70126de8eaf65..b454bdcfa7edcc572e6ca1af98479966e067bd09 100644
--- a/sys/net/gnrc/network_layer/sixlowpan/nd/gnrc_sixlowpan_nd.c
+++ b/sys/net/gnrc/network_layer/sixlowpan/nd/gnrc_sixlowpan_nd.c
@@ -12,6 +12,8 @@
  * @file
  */
 
+#include <string.h>
+
 #include "net/eui64.h"
 #include "net/icmpv6.h"
 #include "net/gnrc/ipv6.h"
diff --git a/sys/net/gnrc/routing/rpl/gnrc_rpl.c b/sys/net/gnrc/routing/rpl/gnrc_rpl.c
index a6a0b2a96cafa1e750ecd9c7b49f6b5b7ab76f4d..8c4b1a9ac31ddbe9b573fb286692a4b0807671c5 100644
--- a/sys/net/gnrc/routing/rpl/gnrc_rpl.c
+++ b/sys/net/gnrc/routing/rpl/gnrc_rpl.c
@@ -15,6 +15,8 @@
  * @author  Cenk Gündoğan <cenk.guendogan@haw-hamburg.de>
  */
 
+#include <string.h>
+
 #include "net/icmpv6.h"
 #include "net/ipv6.h"
 #include "net/gnrc/netif/internal.h"
diff --git a/sys/net/gnrc/routing/rpl/gnrc_rpl_control_messages.c b/sys/net/gnrc/routing/rpl/gnrc_rpl_control_messages.c
index 6224a06c4230857e694c8fe062cd0a6308ca7770..ac9b57be1cbddeb83f49e0b41705c5bf1fe2f561 100644
--- a/sys/net/gnrc/routing/rpl/gnrc_rpl_control_messages.c
+++ b/sys/net/gnrc/routing/rpl/gnrc_rpl_control_messages.c
@@ -16,6 +16,8 @@
  * @author Cenk Gündoğan <cenk.guendogan@haw-hamburg.de>
  */
 
+#include <string.h>
+
 #include "net/af.h"
 #include "net/icmpv6.h"
 #include "net/ipv6/hdr.h"
diff --git a/sys/net/gnrc/routing/rpl/gnrc_rpl_dodag.c b/sys/net/gnrc/routing/rpl/gnrc_rpl_dodag.c
index 9fbe1bcf470a9dd29b6d47f6ca2e18b69479041f..c32074155a2c8ae307e073ca88d4b1f7f93e4171 100644
--- a/sys/net/gnrc/routing/rpl/gnrc_rpl_dodag.c
+++ b/sys/net/gnrc/routing/rpl/gnrc_rpl_dodag.c
@@ -17,6 +17,8 @@
  */
 
 #include <stdbool.h>
+#include <string.h>
+
 #include "net/af.h"
 #include "net/gnrc/ipv6.h"
 #include "net/gnrc/netif/internal.h"
diff --git a/sys/net/gnrc/routing/rpl/p2p/gnrc_rpl_p2p.c b/sys/net/gnrc/routing/rpl/p2p/gnrc_rpl_p2p.c
index 9d8eaca00d577a888d1162d7434a00a07f614aff..8c7bebd35fba224cbef6064ee392a9c7733cf73d 100644
--- a/sys/net/gnrc/routing/rpl/p2p/gnrc_rpl_p2p.c
+++ b/sys/net/gnrc/routing/rpl/p2p/gnrc_rpl_p2p.c
@@ -14,6 +14,8 @@
  * @author  Cenk Gündoğan <cenk.guendogan@haw-hamburg.de>
  */
 
+#include <string.h>
+
 #include "net/icmpv6.h"
 #include "net/gnrc/ipv6.h"
 #include "net/gnrc/icmpv6.h"
diff --git a/sys/net/gnrc/sock/ip/gnrc_sock_ip.c b/sys/net/gnrc/sock/ip/gnrc_sock_ip.c
index fa73bdcfe100a85d2bdd8d46395ea4bbb4cbce6b..6ba232480aa64f44bb9c90592490fd74c291e838 100644
--- a/sys/net/gnrc/sock/ip/gnrc_sock_ip.c
+++ b/sys/net/gnrc/sock/ip/gnrc_sock_ip.c
@@ -16,6 +16,7 @@
  */
 
 #include <errno.h>
+#include <string.h>
 
 #include "byteorder.h"
 #include "net/af.h"
diff --git a/sys/net/gnrc/sock/udp/gnrc_sock_udp.c b/sys/net/gnrc/sock/udp/gnrc_sock_udp.c
index 41831e22b64b281e9b6088df5fb79df3c807f728..228aa780956c96f93a3443bfbf271692d3e70faf 100644
--- a/sys/net/gnrc/sock/udp/gnrc_sock_udp.c
+++ b/sys/net/gnrc/sock/udp/gnrc_sock_udp.c
@@ -16,6 +16,7 @@
  */
 
 #include <errno.h>
+#include <string.h>
 
 #include "byteorder.h"
 #include "net/af.h"
diff --git a/sys/net/gnrc/transport_layer/tcp/gnrc_tcp.c b/sys/net/gnrc/transport_layer/tcp/gnrc_tcp.c
index 7e824ac976a12e52de9408a49d40461c77904216..15a2401250b951af0a30247637e9cb21fbc10118 100644
--- a/sys/net/gnrc/transport_layer/tcp/gnrc_tcp.c
+++ b/sys/net/gnrc/transport_layer/tcp/gnrc_tcp.c
@@ -18,8 +18,9 @@
  */
 
 #include <errno.h>
-#include <utlist.h>
 #include <string.h>
+#include <utlist.h>
+
 #include "net/af.h"
 #include "net/gnrc.h"
 #include "net/gnrc/tcp.h"
diff --git a/sys/net/routing/nhdp/iib_table.c b/sys/net/routing/nhdp/iib_table.c
index e1ee9e9ad95e13e351556ef215ade04234d69c4b..4b7570ec5062da4d8eb8fe2850e9e76b199b551d 100644
--- a/sys/net/routing/nhdp/iib_table.c
+++ b/sys/net/routing/nhdp/iib_table.c
@@ -18,6 +18,8 @@
  * @}
  */
 
+#include <string.h>
+
 #include "mutex.h"
 #include "timex.h"
 #include "xtimer.h"
diff --git a/sys/net/routing/nhdp/nhdp.c b/sys/net/routing/nhdp/nhdp.c
index 0897c812723dc41c76720e0452369565c7eb5021..34488377c6b2dd088dbf30da33f6471268e0edd9 100644
--- a/sys/net/routing/nhdp/nhdp.c
+++ b/sys/net/routing/nhdp/nhdp.c
@@ -18,6 +18,8 @@
  * @}
  */
 
+#include <string.h>
+
 #include "net/sock/udp.h"
 #include "msg.h"
 #include "net/gnrc/netapi.h"
diff --git a/sys/random/fortuna.c b/sys/random/fortuna.c
index 01ac4fa5db91bee154906175c0bb3355e8094ff2..b7e4ee31c925866d748b4d513d8459477e0da02d 100644
--- a/sys/random/fortuna.c
+++ b/sys/random/fortuna.c
@@ -17,6 +17,8 @@
  * @}
  */
 
+#include <string.h>
+
 #include "log.h"
 #include "mutex.h"
 
diff --git a/sys/random/fortuna/fortuna.c b/sys/random/fortuna/fortuna.c
index 2a60865978978fd4b8e01e5a46c52c2a291fa4a7..f1d801dd26ef107f8bb0096b85f032587e48edb9 100755
--- a/sys/random/fortuna/fortuna.c
+++ b/sys/random/fortuna/fortuna.c
@@ -5,6 +5,8 @@
  * for more information.
  */
 
+#include <string.h>
+
 #include "fortuna.h"
 
 /**
diff --git a/sys/shell/commands/sc_ccnl.c b/sys/shell/commands/sc_ccnl.c
index a522d2f8dbb30d833228f245d0d41eda15c83284..249c840a25f928f721297a04d659278a47c54059 100644
--- a/sys/shell/commands/sc_ccnl.c
+++ b/sys/shell/commands/sc_ccnl.c
@@ -18,6 +18,8 @@
  * @}
  */
 
+#include <string.h>
+
 #include "random.h"
 #include "sched.h"
 #include "net/gnrc/netif.h"
diff --git a/sys/shell/commands/sc_gnrc_netif.c b/sys/shell/commands/sc_gnrc_netif.c
index 39e37bbfe8053417586b20fc5adb8a7f98db8f7d..3bfe89a24cab1c9601af8b6cecdf9466227cdfdd 100644
--- a/sys/shell/commands/sc_gnrc_netif.c
+++ b/sys/shell/commands/sc_gnrc_netif.c
@@ -19,6 +19,7 @@
  */
 
 #include <stdio.h>
+#include <string.h>
 
 #include "net/ipv6/addr.h"
 #include "net/gnrc.h"