diff --git a/internal/sys.hpp b/internal/sys.hpp
index 98221c3..98b6e5c 100644
--- a/internal/sys.hpp
+++ b/internal/sys.hpp
@@ -27,9 +27,9 @@
 
     virtual int open(const char* pathname, int flags) const = 0;
     virtual int close(int fd) const = 0;
-    virtual void* mmap(void* addr, size_t length, int prot, int flags, int fd,
-                       off_t offset) const = 0;
-    virtual int munmap(void* addr, size_t length) const = 0;
+    virtual void* mmap(void* addr, std::size_t length, int prot, int flags,
+                       int fd, off_t offset) const = 0;
+    virtual int munmap(void* addr, std::size_t length) const = 0;
     virtual int getpagesize() const = 0;
     virtual int ioctl(int fd, unsigned long request, void* param) const = 0;
     virtual int poll(struct pollfd* fds, nfds_t nfds, int timeout) const = 0;
@@ -45,9 +45,9 @@
   public:
     int open(const char* pathname, int flags) const override;
     int close(int fd) const override;
-    void* mmap(void* addr, size_t length, int prot, int flags, int fd,
+    void* mmap(void* addr, std::size_t length, int prot, int flags, int fd,
                off_t offset) const override;
-    int munmap(void* addr, size_t length) const override;
+    int munmap(void* addr, std::size_t length) const override;
     int getpagesize() const override;
     int ioctl(int fd, unsigned long request, void* param) const override;
     int poll(struct pollfd* fds, nfds_t nfds, int timeout) const override;