diff --git a/src/base/BUILD.bazel b/src/base/BUILD.bazel
index f3bfdd0c6..f121b3401 100644
--- a/src/base/BUILD.bazel
+++ b/src/base/BUILD.bazel
@@ -644,19 +644,12 @@ cc_test_mozc(
     ],
 )
 
-cc_library_mozc(
-    name = "mmap_sync_interface",
-    hdrs = ["mmap_sync_interface.h"],
-    visibility = ["//visibility:private"],
-)
-
 cc_library_mozc(
     name = "mmap",
     srcs = ["mmap.cc"],
     hdrs = ["mmap.h"],
     deps = [
         ":logging",
-        ":mmap_sync_interface",
         ":port",
         ":scoped_handle",
         ":util",
diff --git a/src/base/mmap.h b/src/base/mmap.h
index 93b52642b..f7ced76fe 100644
--- a/src/base/mmap.h
+++ b/src/base/mmap.h
@@ -30,18 +30,18 @@
 #ifndef MOZC_BASE_MMAP_H_
 #define MOZC_BASE_MMAP_H_
 
-#include <string>
-
-#include "base/mmap_sync_interface.h"
-#include "base/port.h"
-
+#include <cstddef>
 
 namespace mozc {
 
-class Mmap : public MmapSyncInterface {
+class Mmap final {
  public:
   Mmap();
-  ~Mmap() override { Close(); }
+
+  Mmap(const Mmap &) = delete;
+  Mmap &operator=(const Mmap &) = delete;
+
+  ~Mmap() { Close(); }
 
   bool Open(const char *filename, const char *mode = "r");
   void Close();
@@ -73,8 +73,6 @@ class Mmap : public MmapSyncInterface {
  private:
   char *text_;
   size_t size_;
-
-  DISALLOW_COPY_AND_ASSIGN(Mmap);
 };
 
 }  // namespace mozc
diff --git a/src/base/mmap_sync_interface.h b/src/base/mmap_sync_interface.h
deleted file mode 100644
index 907a38c3c..000000000
--- a/src/base/mmap_sync_interface.h
+++ /dev/null
@@ -1,44 +0,0 @@
-// Copyright 2010-2021, Google Inc.
-// All rights reserved.
-//
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions are
-// met:
-//
-//     * Redistributions of source code must retain the above copyright
-// notice, this list of conditions and the following disclaimer.
-//     * Redistributions in binary form must reproduce the above
-// copyright notice, this list of conditions and the following disclaimer
-// in the documentation and/or other materials provided with the
-// distribution.
-//     * Neither the name of Google Inc. nor the names of its
-// contributors may be used to endorse or promote products derived from
-// this software without specific prior written permission.
-//
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-
-#ifndef MOZC_BASE_MMAP_SYNC_INTERFACE_H_
-#define MOZC_BASE_MMAP_SYNC_INTERFACE_H_
-
-namespace mozc {
-
-// This interface is used to resolve a cyclic dependency between PepperFileUtil
-// and Mmap.
-class MmapSyncInterface {
- public:
-  virtual ~MmapSyncInterface() {}
-};
-
-}  // namespace mozc
-
-#endif  // MOZC_BASE_MMAP_SYNC_INTERFACE_H_