diff --git a/t/t_hmac_sha1.c b/t/t_hmac_sha1.c
index 2c22e27..f9e7b76 100644
--- a/t/t_hmac_sha1.c
+++ b/t/t_hmac_sha1.c
@@ -33,6 +33,7 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 #include <cryb/test.h>
 
diff --git a/t/t_hmac_sha224.c b/t/t_hmac_sha224.c
index 36af581..094389d 100644
--- a/t/t_hmac_sha224.c
+++ b/t/t_hmac_sha224.c
@@ -33,6 +33,7 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 #include <cryb/test.h>
 
diff --git a/t/t_hmac_sha256.c b/t/t_hmac_sha256.c
index 44347f2..24cdc9e 100644
--- a/t/t_hmac_sha256.c
+++ b/t/t_hmac_sha256.c
@@ -33,6 +33,7 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 #include <cryb/test.h>
 
diff --git a/t/t_hmac_sha384.c b/t/t_hmac_sha384.c
index 1e9b93e..f24a499 100644
--- a/t/t_hmac_sha384.c
+++ b/t/t_hmac_sha384.c
@@ -33,6 +33,7 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 #include <cryb/test.h>
 
diff --git a/t/t_hmac_sha512.c b/t/t_hmac_sha512.c
index 5855a06..4755c0d 100644
--- a/t/t_hmac_sha512.c
+++ b/t/t_hmac_sha512.c
@@ -33,6 +33,7 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 #include <cryb/test.h>