diff --git a/base/include/android-base/file.h b/base/include/android-base/file.h
index 8f9bf80..86d537d 100644
--- a/base/include/android-base/file.h
+++ b/base/include/android-base/file.h
@@ -20,6 +20,8 @@
 #include <sys/types.h>
 #include <string>
 
+#include "android-base/off64_t.h"
+
 #if !defined(_WIN32) && !defined(O_BINARY)
 /** Windows needs O_BINARY, but Unix never mangles line endings. */
 #define O_BINARY 0
@@ -30,11 +32,6 @@
 #define O_CLOEXEC O_NOINHERIT
 #endif
 
-#if defined(__APPLE__)
-/** Mac OS has always had a 64-bit off_t, so it doesn't have off64_t. */
-typedef off_t off64_t;
-#endif
-
 namespace android {
 namespace base {
 
diff --git a/base/include/android-base/mapped_file.h b/base/include/android-base/mapped_file.h
index 667ba7e..80513b1 100644
--- a/base/include/android-base/mapped_file.h
+++ b/base/include/android-base/mapped_file.h
@@ -16,12 +16,8 @@
 
 #pragma once
 
-#if __APPLE__
-/* Temporary Mac build fix for off64_t. TODO: refactor into `portability.h`. */
-#include "android-base/file.h"
-#endif
-
 #include "android-base/macros.h"
+#include "android-base/off64_t.h"
 
 #include <sys/types.h>
 
diff --git a/base/include/android-base/off64_t.h b/base/include/android-base/off64_t.h
new file mode 100644
index 0000000..e6b71b8
--- /dev/null
+++ b/base/include/android-base/off64_t.h
@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#if defined(__APPLE__)
+/** Mac OS has always had a 64-bit off_t, so it doesn't have off64_t. */
+typedef off_t off64_t;
+#endif