diff --git a/include/unistd.h b/include/unistd.h
index 793af31..56e9ae5 100644
--- a/include/unistd.h
+++ b/include/unistd.h
@@ -51,6 +51,8 @@
 #define _XOPEN_ENH_I18N 700
 #define _XOPEN_SHM 700
 
+#include <stddef.h>
+
 #define R_OK 01
 #define W_OK 02
 #define X_OK 04
@@ -63,4 +65,11 @@
 #define F_TLOCK 03
 #define F_ULOCK 04
 
+#include <types/pid_t.h>
+
+pid_t fork(void);
+int execv(const char *, char *const []);
+int execve(const char *, char *const [], char *const []);
+int execvp(const char *, char *const []);
+
 #endif