diff --git a/src/fcntl/fcntl.c b/src/fcntl/fcntl.c
index 4c34ba0..7b30d2a 100644
--- a/src/fcntl/fcntl.c
+++ b/src/fcntl/fcntl.c
@@ -9,15 +9,48 @@ int fcntl(int fd, int cmd, ...)
 {
 	long arg;
 	va_list ap;
+
 	va_start(ap, cmd);
-	arg = va_arg(ap, long);
+	switch (cmd) {
+	case F_DUPFD:
+	case F_DUPFD_CLOEXEC:
+	case F_SETFD:
+	case F_SETFL:
+	case F_SETOWN:
+	case F_SETSIG:
+	case F_SETLEASE:
+	case F_NOTIFY:
+	case F_SETPIPE_SZ:
+		arg = va_arg(ap, int);
+		break;
+	case F_GETFD:
+	case F_GETFL:
+	case F_GETOWN:
+	case F_GETSIG:
+	case F_GETLEASE:
+	case F_GETPIPE_SZ:
+		arg = 0;
+		break;
+	case F_SETLK:
+	case F_SETLKW:
+	case F_GETLK:
+		arg = (long)va_arg(ap, struct flock *);
+		break;
+	case F_GETOWN_EX:
+	case F_SETOWN_EX:
+		arg = (long)va_arg(ap, struct f_owner_ex *);
+		break;
+	default:
+		arg = va_arg(ap, long);
+	}
 	va_end(ap);
+
 	if (cmd == F_SETFL) arg |= O_LARGEFILE;
-	if (cmd == F_SETLKW) return syscall_cp(SYS_fcntl, fd, cmd, arg);
+	if (cmd == F_SETLKW) return syscall_cp(SYS_fcntl, fd, cmd, (void *)arg);
 	if (cmd == F_GETOWN) {
 		struct f_owner_ex ex;
 		int ret = __syscall(SYS_fcntl, fd, F_GETOWN_EX, &ex);
-		if (ret == -EINVAL) return __syscall(SYS_fcntl, fd, cmd, arg);
+		if (ret == -EINVAL) return __syscall(SYS_fcntl, fd, cmd, (void *)arg);
 		if (ret) return __syscall_ret(ret);
 		return ex.type == F_OWNER_PGRP ? -ex.pid : ex.pid;
 	}
@@ -37,5 +70,14 @@ int fcntl(int fd, int cmd, ...)
 		if (ret >= 0) __syscall(SYS_fcntl, ret, F_SETFD, FD_CLOEXEC);
 		return __syscall_ret(ret);
 	}
-	return syscall(SYS_fcntl, fd, cmd, arg);
+	switch (cmd) {
+	case F_SETLK:
+	case F_SETLKW:
+	case F_GETLK:
+	case F_GETOWN_EX:
+	case F_SETOWN_EX:
+		return syscall(SYS_fcntl, fd, cmd, (void *)arg);
+	default:
+		return syscall(SYS_fcntl, fd, cmd, arg);
+	}
 }