diff --git a/HISTORY.md b/HISTORY.md
index f2a6c58b3..1bb490255 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -2,6 +2,7 @@
 ## Unreleased
 ### Bug Fixes
 * Fixed a race condition for `alive_log_files_` in non-two-write-queues mode. The race is between the write_thread_ in WriteToWAL() and another thread executing `FindObsoleteFiles()`. The race condition will be caught if `__glibcxx_requires_nonempty` is enabled.
+* Fixed a race condition when mmaping a WritableFile on POSIX.
 
 ## 6.29.4 (03/22/2022)
 ### Bug Fixes
diff --git a/env/fs_posix.cc b/env/fs_posix.cc
index db5319615..ab4dead50 100644
--- a/env/fs_posix.cc
+++ b/env/fs_posix.cc
@@ -325,14 +325,7 @@ class PosixFileSystem : public FileSystem {
     SetFD_CLOEXEC(fd, &options);
 
     if (options.use_mmap_writes) {
-      if (!checkedDiskForMmap_) {
-        // this will be executed once in the program's lifetime.
-        // do not use mmapWrite on non ext-3/xfs/tmpfs systems.
-        if (!SupportsFastAllocate(fname)) {
-          forceMmapOff_ = true;
-        }
-        checkedDiskForMmap_ = true;
-      }
+      MaybeForceDisableMmap(fd);
     }
     if (options.use_mmap_writes && !forceMmapOff_) {
       result->reset(new PosixMmapFile(fname, fd, page_size_, options));
@@ -431,14 +424,7 @@ class PosixFileSystem : public FileSystem {
     }
 
     if (options.use_mmap_writes) {
-      if (!checkedDiskForMmap_) {
-        // this will be executed once in the program's lifetime.
-        // do not use mmapWrite on non ext-3/xfs/tmpfs systems.
-        if (!SupportsFastAllocate(fname)) {
-          forceMmapOff_ = true;
-        }
-        checkedDiskForMmap_ = true;
-      }
+      MaybeForceDisableMmap(fd);
     }
     if (options.use_mmap_writes && !forceMmapOff_) {
       result->reset(new PosixMmapFile(fname, fd, page_size_, options));
@@ -999,8 +985,7 @@ class PosixFileSystem : public FileSystem {
   }
 #endif
  private:
-  bool checkedDiskForMmap_;
-  bool forceMmapOff_;  // do we override Env options?
+  bool forceMmapOff_ = false;  // do we override Env options?
 
   // Returns true iff the named directory exists and is a directory.
   virtual bool DirExists(const std::string& dname) {
@@ -1011,10 +996,10 @@ class PosixFileSystem : public FileSystem {
     return false;  // stat() failed return false
   }
 
-  bool SupportsFastAllocate(const std::string& path) {
+  bool SupportsFastAllocate(int fd) {
 #ifdef ROCKSDB_FALLOCATE_PRESENT
     struct statfs s;
-    if (statfs(path.c_str(), &s)) {
+    if (fstatfs(fd, &s)) {
       return false;
     }
     switch (s.f_type) {
@@ -1028,11 +1013,26 @@ class PosixFileSystem : public FileSystem {
         return false;
     }
 #else
-    (void)path;
+    (void)fd;
     return false;
 #endif
   }
 
+  void MaybeForceDisableMmap(int fd) {
+    static std::once_flag s_check_disk_for_mmap_once;
+    assert(this == FileSystem::Default().get());
+    std::call_once(
+        s_check_disk_for_mmap_once,
+        [this](int fdesc) {
+          // this will be executed once in the program's lifetime.
+          // do not use mmapWrite on non ext-3/xfs/tmpfs systems.
+          if (!SupportsFastAllocate(fdesc)) {
+            forceMmapOff_ = true;
+          }
+        },
+        fd);
+  }
+
 #ifdef ROCKSDB_IOURING_PRESENT
   bool IsIOUringEnabled() {
     if (RocksDbIOUringEnable && RocksDbIOUringEnable()) {
@@ -1096,8 +1096,7 @@ size_t PosixFileSystem::GetLogicalBlockSizeForWriteIfNeeded(
 }
 
 PosixFileSystem::PosixFileSystem()
-    : checkedDiskForMmap_(false),
-      forceMmapOff_(false),
+    : forceMmapOff_(false),
       page_size_(getpagesize()),
       allow_non_owner_access_(true) {
 #if defined(ROCKSDB_IOURING_PRESENT)