diff --git a/libc/bionic/mmap.cpp b/libc/bionic/mmap.cpp
index 75bea58..84a0f76 100644
--- a/libc/bionic/mmap.cpp
+++ b/libc/bionic/mmap.cpp
@@ -55,5 +55,5 @@
 }
 
 void* mmap(void* addr, size_t size, int prot, int flags, int fd, off_t offset) {
-  return mmap64(addr, size, prot, flags, fd, static_cast<off64_t>(offset));
+  return mmap64(addr, size, prot, flags, fd, static_cast<off64_t>(offset) & 0xffffffff);
 }