diff --git a/auth-options.c b/auth-options.c
index b05d6d6f..d1f42f04 100644
--- a/auth-options.c
+++ b/auth-options.c
@@ -26,6 +26,7 @@
 #include <stdarg.h>
 #include <ctype.h>
 #include <limits.h>
+#include <stdlib.h>
 
 #include "openbsd-compat/sys-queue.h"
 
diff --git a/hmac.c b/hmac.c
index 1c879640..a29f32c5 100644
--- a/hmac.c
+++ b/hmac.c
@@ -19,6 +19,7 @@
 
 #include <sys/types.h>
 #include <string.h>
+#include <stdlib.h>
 
 #include "sshbuf.h"
 #include "digest.h"
diff --git a/krl.c b/krl.c
index 8e2d5d5d..c32e147a 100644
--- a/krl.c
+++ b/krl.c
@@ -28,6 +28,7 @@
 #include <string.h>
 #include <time.h>
 #include <unistd.h>
+#include <stdlib.h>
 
 #include "sshbuf.h"
 #include "ssherr.h"
diff --git a/mac.c b/mac.c
index 51dc11d7..3d11eba6 100644
--- a/mac.c
+++ b/mac.c
@@ -29,6 +29,7 @@
 
 #include <string.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 #include "digest.h"
 #include "hmac.h"