diff --git a/utilities/fault_injection_fs.cc b/utilities/fault_injection_fs.cc
index 5943ebb24..26d4d2d4c 100644
--- a/utilities/fault_injection_fs.cc
+++ b/utilities/fault_injection_fs.cc
@@ -240,6 +240,7 @@ IOStatus TestFSWritableFile::PositionedAppend(
 
 IOStatus TestFSWritableFile::Close(const IOOptions& options,
                                    IODebugContext* dbg) {
+  MutexLock l(&mutex_);
   if (!fs_->IsFilesystemActive()) {
     return fs_->GetError();
   }
@@ -271,6 +272,7 @@ IOStatus TestFSWritableFile::Close(const IOOptions& options,
 }
 
 IOStatus TestFSWritableFile::Flush(const IOOptions&, IODebugContext*) {
+  MutexLock l(&mutex_);
   if (!fs_->IsFilesystemActive()) {
     return fs_->GetError();
   }
@@ -282,6 +284,7 @@ IOStatus TestFSWritableFile::Flush(const IOOptions&, IODebugContext*) {
 
 IOStatus TestFSWritableFile::Sync(const IOOptions& options,
                                   IODebugContext* dbg) {
+  MutexLock l(&mutex_);
   if (!fs_->IsFilesystemActive()) {
     return fs_->GetError();
   }
@@ -302,6 +305,7 @@ IOStatus TestFSWritableFile::Sync(const IOOptions& options,
 IOStatus TestFSWritableFile::RangeSync(uint64_t offset, uint64_t nbytes,
                                        const IOOptions& options,
                                        IODebugContext* dbg) {
+  MutexLock l(&mutex_);
   if (!fs_->IsFilesystemActive()) {
     return fs_->GetError();
   }
diff --git a/utilities/fault_injection_fs.h b/utilities/fault_injection_fs.h
index 886234eed..8cf6c44c8 100644
--- a/utilities/fault_injection_fs.h
+++ b/utilities/fault_injection_fs.h
@@ -97,7 +97,7 @@ class TestFSWritableFile : public FSWritableFile {
   };
 
  private:
-  FSFileState state_;
+  FSFileState state_;  // Need protection by mutex_
   FileOptions file_opts_;
   std::unique_ptr<FSWritableFile> target_;
   bool writable_file_opened_;