diff --git a/unit/rilmodem-test-engine.c b/unit/rilmodem-test-engine.c
index c5693607..7cbc1ad4 100644
--- a/unit/rilmodem-test-engine.c
+++ b/unit/rilmodem-test-engine.c
@@ -29,6 +29,7 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <unistd.h>
+#include <string.h>
 
 #include <ofono/types.h>
 
diff --git a/unit/rilmodem-test-server.c b/unit/rilmodem-test-server.c
index 17e5090e..5a3b03a0 100644
--- a/unit/rilmodem-test-server.c
+++ b/unit/rilmodem-test-server.c
@@ -28,6 +28,7 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <unistd.h>
+#include <string.h>
 
 #include <ofono/types.h>
 
diff --git a/unit/test-rilmodem-cs.c b/unit/test-rilmodem-cs.c
index bfa2a722..ae7abec1 100644
--- a/unit/test-rilmodem-cs.c
+++ b/unit/test-rilmodem-cs.c
@@ -32,6 +32,7 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <unistd.h>
+#include <string.h>
 
 #include <ofono/modem.h>
 #include <ofono/types.h>
diff --git a/unit/test-rilmodem-sms.c b/unit/test-rilmodem-sms.c
index 1ed1b519..70c7386c 100644
--- a/unit/test-rilmodem-sms.c
+++ b/unit/test-rilmodem-sms.c
@@ -32,6 +32,7 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <unistd.h>
+#include <string.h>
 
 #include <ofono/modem.h>
 #include <ofono/types.h>