diff --git a/unix/uxproxy.c b/unix/uxproxy.c
index 617f5ccf..209991fc 100644
--- a/unix/uxproxy.c
+++ b/unix/uxproxy.c
@@ -281,7 +281,7 @@ Socket platform_new_connection(SockAddr addr, char *hostname,
 	    close(i);
 	fcntl(0, F_SETFD, 0);
 	fcntl(1, F_SETFD, 0);
-	execl("/bin/sh", "sh", "-c", cmd, NULL);
+	execl("/bin/sh", "sh", "-c", cmd, (void *)NULL);
 	_exit(255);
     }
 
diff --git a/unix/uxpty.c b/unix/uxpty.c
index f91dc716..37a017d3 100644
--- a/unix/uxpty.c
+++ b/unix/uxpty.c
@@ -813,7 +813,7 @@ static const char *pty_init(void *frontend, void **backend_handle, Config *cfg,
 		sprintf(shellname, "-%s", p);
 	    } else
 		shellname = shell;
-	    execl(getenv("SHELL"), shellname, NULL);
+	    execl(getenv("SHELL"), shellname, (void *)NULL);
 	}
 
 	/*