diff --git a/src/library_sigs.js b/src/library_sigs.js
index 8fa6fecb7dd39..8c79c108679d2 100644
--- a/src/library_sigs.js
+++ b/src/library_sigs.js
@@ -353,9 +353,9 @@ sigs = {
   _gmtime_js__sig: 'vpp',
   _localtime_js__sig: 'vpp',
   _mktime_js__sig: 'ip',
-  _mmap_js__sig: 'ipiiippp',
-  _msync_js__sig: 'ippiiip',
-  _munmap_js__sig: 'ippiiip',
+  _mmap_js__sig: 'ipiiijpp',
+  _msync_js__sig: 'ippiiij',
+  _munmap_js__sig: 'ippiiij',
   _setitimer_js__sig: 'iid',
   _timegm_js__sig: 'ip',
   _tzset_js__sig: 'vppp',
diff --git a/src/library_syscall.js b/src/library_syscall.js
index 2eaabe5e74a38..992cedf78ee54 100644
--- a/src/library_syscall.js
+++ b/src/library_syscall.js
@@ -133,11 +133,12 @@ var SyscallsLibrary = {
     '$mmapAlloc',
     'emscripten_builtin_memalign',
 #endif
-  ],
-  _mmap_js: function(len, prot, flags, fd, off, allocated, addr) {
+  ].concat(i53ConversionDeps),
+  _mmap_js: function(len, prot, flags, fd, {{{ defineI64Param('offset') }}}, allocated, addr) {
+    {{{ receiveI64ParamAsI53('offset', -cDefs.EOVERFLOW) }}}
 #if FILESYSTEM && SYSCALLS_REQUIRE_FILESYSTEM
     var stream = SYSCALLS.getStreamFromFD(fd);
-    var res = FS.mmap(stream, len, off, prot, flags);
+    var res = FS.mmap(stream, len, offset, prot, flags);
     var ptr = res.ptr;
     {{{ makeSetValue('allocated', 0, 'res.allocated', 'i32') }}};
 #if CAN_ADDRESS_2GB
@@ -154,8 +155,9 @@ var SyscallsLibrary = {
 #if FILESYSTEM && SYSCALLS_REQUIRE_FILESYSTEM
     '$FS',
 #endif
-  ],
-  _munmap_js: function(addr, len, prot, flags, fd, offset) {
+  ].concat(i53ConversionDeps),
+  _munmap_js: function(addr, len, prot, flags, fd, {{{ defineI64Param('offset') }}}) {
+    {{{ receiveI64ParamAsI53('offset', -cDefs.EOVERFLOW) }}}
 #if FILESYSTEM && SYSCALLS_REQUIRE_FILESYSTEM
     var stream = SYSCALLS.getStreamFromFD(fd);
     if (prot & {{{ cDefs.PROT_WRITE }}}) {
@@ -623,8 +625,10 @@ var SyscallsLibrary = {
 
     return total;
   },
-  _msync_js: function(addr, len, prot, flags, fd, offset) {
-    SYSCALLS.doMsync(addr, SYSCALLS.getStreamFromFD(fd), len, flags, 0);
+  _msync_js__deps: i53ConversionDeps,
+  _msync_js: function(addr, len, prot, flags, fd, {{{ defineI64Param('offset') }}}) {
+    {{{ receiveI64ParamAsI53('offset', -cDefs.EOVERFLOW) }}}
+    SYSCALLS.doMsync(addr, SYSCALLS.getStreamFromFD(fd), len, flags, offset);
     return 0;
   },
   __syscall_fdatasync: function(fd) {
diff --git a/system/lib/libc/emscripten_internal.h b/system/lib/libc/emscripten_internal.h
index 0d878c49ebe47..ceef9c2984d24 100644
--- a/system/lib/libc/emscripten_internal.h
+++ b/system/lib/libc/emscripten_internal.h
@@ -75,13 +75,13 @@ int _mmap_js(size_t length,
              int prot,
              int flags,
              int fd,
-             size_t offset,
+             off_t offset,
              int* allocated,
              void** addr);
 int _munmap_js(
-  intptr_t addr, size_t length, int prot, int flags, int fd, size_t offset);
+  intptr_t addr, size_t length, int prot, int flags, int fd, off_t offset);
 int _msync_js(
-  intptr_t addr, size_t length, int prot, int flags, int fd, size_t offset);
+  intptr_t addr, size_t length, int prot, int flags, int fd, off_t offset);
 
 struct dso;
 
diff --git a/system/lib/libc/emscripten_mmap.c b/system/lib/libc/emscripten_mmap.c
index 01ee6530c378e..2cca5eeee6275 100644
--- a/system/lib/libc/emscripten_mmap.c
+++ b/system/lib/libc/emscripten_mmap.c
@@ -105,13 +105,13 @@ int __syscall_msync(intptr_t addr, size_t len, int flags) {
   return _msync_js(addr, len, map->prot, map->flags, map->fd, map->offset);
 }
 
-intptr_t __syscall_mmap2(intptr_t addr, size_t len, int prot, int flags, int fd, size_t off) {
+intptr_t __syscall_mmap2(intptr_t addr, size_t len, int prot, int flags, int fd, off_t offset) {
   if (addr != 0) {
     // We don't currently support location hints for the address of the mapping
     return -EINVAL;
   }
 
-  off *= SYSCALL_MMAP2_UNIT;
+  offset *= SYSCALL_MMAP2_UNIT;
   struct map* new_map;
 
   // MAP_ANONYMOUS (aka MAP_ANON) isn't actually defined by POSIX spec,
@@ -132,7 +132,7 @@ intptr_t __syscall_mmap2(intptr_t addr, size_t len, int prot, int flags, int fd,
   } else {
     new_map = emscripten_builtin_malloc(sizeof(struct map));
     int rtn =
-      _mmap_js(len, prot, flags, fd, off, &new_map->allocated, &new_map->addr);
+      _mmap_js(len, prot, flags, fd, offset, &new_map->allocated, &new_map->addr);
     if (rtn < 0) {
       emscripten_builtin_free(new_map);
       return rtn;
@@ -142,7 +142,7 @@ intptr_t __syscall_mmap2(intptr_t addr, size_t len, int prot, int flags, int fd,
 
   new_map->length = len;
   new_map->flags = flags;
-  new_map->offset = off;
+  new_map->offset = offset;
   new_map->prot = prot;
 
   LOCK(lock);
diff --git a/system/lib/libc/musl/arch/emscripten/syscall_arch.h b/system/lib/libc/musl/arch/emscripten/syscall_arch.h
index 89dcfeadc7188..b72e1f738ebe3 100644
--- a/system/lib/libc/musl/arch/emscripten/syscall_arch.h
+++ b/system/lib/libc/musl/arch/emscripten/syscall_arch.h
@@ -1,6 +1,6 @@
+#include <sys/types.h>
 #include <wasi/api.h>
 #include <wasi/wasi-helpers.h>
-#include <emscripten/em_macros.h>
 
 // Compile as if we can pass uint64 values directly to the
 // host.  Binaryen will take care of splitting any i64 params
@@ -55,9 +55,9 @@ int __syscall_mremap(intptr_t old_addr, size_t old_size, size_t new_size, int fl
 int __syscall_poll(intptr_t fds, int nfds, int timeout);
 int __syscall_getcwd(intptr_t buf, size_t size);
 int __syscall_ugetrlimit(int resource, intptr_t rlim);
-intptr_t __syscall_mmap2(intptr_t addr, size_t len, int prot, int flags, int fd, size_t off);
-int __syscall_truncate64(intptr_t path, uint64_t length);
-int __syscall_ftruncate64(int fd, uint64_t length);
+intptr_t __syscall_mmap2(intptr_t addr, size_t len, int prot, int flags, int fd, off_t offset);
+int __syscall_truncate64(intptr_t path, off_t length);
+int __syscall_ftruncate64(int fd, off_t length);
 int __syscall_stat64(intptr_t path, intptr_t buf);
 int __syscall_lstat64(intptr_t path, intptr_t buf);
 int __syscall_fstat64(int fd, intptr_t buf);
@@ -81,7 +81,7 @@ int __syscall_getdents64(int fd, intptr_t dirp, size_t count);
 int __syscall_fcntl64(int fd, int cmd, ...);
 int __syscall_statfs64(intptr_t path, size_t size, intptr_t buf);
 int __syscall_fstatfs64(int fd, size_t size, intptr_t buf);
-int __syscall_fadvise64(int fd, uint64_t offset, uint64_t length, int advice);
+int __syscall_fadvise64(int fd, off_t offset, off_t length, int advice);
 int __syscall_openat(int dirfd, intptr_t path, int flags, ...); // mode is optional
 int __syscall_mkdirat(int dirfd, intptr_t path, int mode);
 int __syscall_mknodat(int dirfd, intptr_t path, int mode, int dev);
@@ -96,7 +96,7 @@ int __syscall_fchmodat(int dirfd, intptr_t path, int mode, ...);
 int __syscall_faccessat(int dirfd, intptr_t path, int amode, int flags);
 int __syscall_pselect6(int nfds, intptr_t readfds, intptr_t writefds, intptr_t exceptfds, intptr_t timeout, intptr_t sigmaks);
 int __syscall_utimensat(int dirfd, intptr_t path, intptr_t times, int flags);
-int __syscall_fallocate(int fd, int mode, int64_t off, int64_t len);
+int __syscall_fallocate(int fd, int mode, off_t offset, off_t len);
 int __syscall_dup3(int fd, int suggestfd, int flags);
 int __syscall_pipe2(intptr_t fds, int flags);
 int __syscall_recvmmsg(int sockfd, intptr_t msgvec, size_t vlen, int flags, ...);
diff --git a/system/lib/standalone/standalone.c b/system/lib/standalone/standalone.c
index 5b9c66564e06b..6a85d7426489c 100644
--- a/system/lib/standalone/standalone.c
+++ b/system/lib/standalone/standalone.c
@@ -74,14 +74,14 @@ weak int _mmap_js(size_t length,
                   int prot,
                   int flags,
                   int fd,
-                  size_t offset,
+                  off_t offset,
                   int* allocated,
                   void** addr) {
   return -ENOSYS;
 }
 
 weak int _munmap_js(
-  intptr_t addr, size_t length, int prot, int flags, int fd, size_t offset) {
+  intptr_t addr, size_t length, int prot, int flags, int fd, off_t offset) {
   return -ENOSYS;
 }
 
diff --git a/system/lib/wasmfs/js_api.cpp b/system/lib/wasmfs/js_api.cpp
index eed0ac60fc30a..f2bd3069eb52f 100644
--- a/system/lib/wasmfs/js_api.cpp
+++ b/system/lib/wasmfs/js_api.cpp
@@ -129,8 +129,8 @@ int _wasmfs_open(char* path, int flags, mode_t mode) {
   return __syscall_openat(AT_FDCWD, (intptr_t)path, flags, mode);
 }
 
-int _wasmfs_allocate(int fd, int64_t off, int64_t len) {
-  return __syscall_fallocate(fd, 0, off, len);
+int _wasmfs_allocate(int fd, off_t offset, off_t len) {
+  return __syscall_fallocate(fd, 0, offset, len);
 }
 
 int _wasmfs_mknod(char* path, mode_t mode, dev_t dev) {
diff --git a/system/lib/wasmfs/syscalls.cpp b/system/lib/wasmfs/syscalls.cpp
index 0e581d7dabe93..7da2cc6d6269e 100644
--- a/system/lib/wasmfs/syscalls.cpp
+++ b/system/lib/wasmfs/syscalls.cpp
@@ -1226,7 +1226,7 @@ static int doTruncate(std::shared_ptr<File>& file, off_t size) {
   return ret;
 }
 
-int __syscall_truncate64(intptr_t path, uint64_t size) {
+int __syscall_truncate64(intptr_t path, off_t size) {
   auto parsed = path::parseFile((char*)path);
   if (auto err = parsed.getError()) {
     return err;
@@ -1234,7 +1234,7 @@ int __syscall_truncate64(intptr_t path, uint64_t size) {
   return doTruncate(parsed.getFile(), size);
 }
 
-int __syscall_ftruncate64(int fd, uint64_t size) {
+int __syscall_ftruncate64(int fd, off_t size) {
   auto openFile = wasmFS.getFileTable().locked().getEntry(fd);
   if (!openFile) {
     return -EBADF;
@@ -1358,7 +1358,7 @@ int __syscall_poll(intptr_t fds_, int nfds, int timeout) {
   return nonzero;
 }
 
-int __syscall_fallocate(int fd, int mode, int64_t off, int64_t len) {
+int __syscall_fallocate(int fd, int mode, off_t offset, off_t len) {
   assert(mode == 0); // TODO, but other modes were never supported in the old FS
 
   auto fileTable = wasmFS.getFileTable().locked();
@@ -1378,14 +1378,14 @@ int __syscall_fallocate(int fd, int mode, int64_t off, int64_t len) {
     return -EBADF;
   }
 
-  if (off < 0 || len <= 0) {
+  if (offset < 0 || len <= 0) {
     return -EINVAL;
   }
 
   // TODO: We could only fill zeros for regions that were completely unused
   //       before, which for a backend with sparse data storage could make a
   //       difference. For that we'd need a new backend API.
-  auto newNeededSize = off + len;
+  auto newNeededSize = offset + len;
   off_t size = locked.getSize();
   if (size < 0) {
     return size;
@@ -1534,7 +1534,7 @@ int _mmap_js(size_t length,
              int prot,
              int flags,
              int fd,
-             size_t offset,
+             off_t offset,
              int* allocated,
              void** addr) {
   // PROT_EXEC is not supported (although we pretend to support the absence of
@@ -1621,7 +1621,7 @@ int _mmap_js(size_t length,
 }
 
 int _msync_js(
-  intptr_t addr, size_t length, int prot, int flags, int fd, size_t offset) {
+  intptr_t addr, size_t length, int prot, int flags, int fd, off_t offset) {
   // TODO: This is not correct! Mappings should be associated with files, not
   // fds. Only need to sync if shared and writes are allowed.
   int mapType = flags & MAP_TYPE;
@@ -1637,7 +1637,7 @@ int _msync_js(
 }
 
 int _munmap_js(
-  intptr_t addr, size_t length, int prot, int flags, int fd, size_t offset) {
+  intptr_t addr, size_t length, int prot, int flags, int fd, off_t offset) {
   // TODO: This is not correct! Mappings should be associated with files, not
   // fds.
   // TODO: Syncing should probably be handled in __syscall_munmap instead.
@@ -1718,7 +1718,7 @@ int __syscall_recvmsg(
   return -ENOSYS;
 }
 
-int __syscall_fadvise64(int fd, uint64_t offset, uint64_t length, int advice) {
+int __syscall_fadvise64(int fd, off_t offset, off_t length, int advice) {
   // Advice is currently ignored. TODO some backends might use it
   return 0;
 }