diff --git a/CMakeLists.txt b/CMakeLists.txt
index 57a0c74..f6a7c0a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -37,6 +37,7 @@ include(CheckCXXSymbolExists)
 # versions of do not expose fdatasync() in <unistd.h> in standard C mode
 # (-std=c11), but do expose the function in standard C++ mode (-std=c++11).
 check_cxx_symbol_exists(fdatasync "unistd.h" HAVE_FDATASYNC)
+check_cxx_symbol_exists(F_FULLFSYNC "fcntl.h" HAVE_FULLFSYNC)
 
 include(CheckCXXSourceCompiles)
 
diff --git a/port/port_config.h.in b/port/port_config.h.in
index 645c78c..d6a6d01 100644
--- a/port/port_config.h.in
+++ b/port/port_config.h.in
@@ -10,6 +10,11 @@
 #cmakedefine01 HAVE_FDATASYNC
 #endif  // !defined(HAVE_FDATASYNC)
 
+// Define to 1 if you have a definition for F_FULLFSYNC in <fcntl.h>.
+#if !defined(HAVE_FULLFSYNC)
+#cmakedefine01 HAVE_FULLFSYNC
+#endif  // !defined(HAVE_FULLFSYNC)
+
 // Define to 1 if you have Google CRC32C.
 #if !defined(HAVE_CRC32C)
 #cmakedefine01 HAVE_CRC32C
diff --git a/util/env_posix.cc b/util/env_posix.cc
index 76bb648..362adb3 100644
--- a/util/env_posix.cc
+++ b/util/env_posix.cc
@@ -35,12 +35,6 @@
 #include "util/posix_logger.h"
 #include "util/env_posix_test_helper.h"
 
-// HAVE_FDATASYNC is defined in the auto-generated port_config.h, which is
-// included by port_stdcxx.h.
-#if !HAVE_FDATASYNC
-#define fdatasync fsync
-#endif  // !HAVE_FDATASYNC
-
 namespace leveldb {
 
 namespace {
@@ -314,10 +308,11 @@ class PosixWritableFile final : public WritableFile {
     }
 
     status = FlushBuffer();
-    if (status.ok() && ::fdatasync(fd_) != 0) {
-      status = PosixError(filename_, errno);
+    if (!status.ok()) {
+      return status;
     }
-    return status;
+
+    return SyncFd(fd_, filename_);
   }
 
  private:
@@ -352,14 +347,41 @@ class PosixWritableFile final : public WritableFile {
     if (fd < 0) {
       status = PosixError(dirname_, errno);
     } else {
-      if (::fsync(fd) < 0) {
-        status = PosixError(dirname_, errno);
-      }
+      status = SyncFd(fd, dirname_);
       ::close(fd);
     }
     return status;
   }
 
+  // Ensures that all the caches associated with the given file descriptor's
+  // data are flushed all the way to durable media, and can withstand power
+  // failures.
+  //
+  // The path argument is only used to populate the description string in the
+  // returned Status if an error occurs.
+  static Status SyncFd(int fd, const std::string& fd_path) {
+#if HAVE_FULLFSYNC
+    // On macOS and iOS, fsync() doesn't guarantee durability past power
+    // failures. fcntl(F_FULLFSYNC) is required for that purpose. Some
+    // filesystems don't support fcntl(F_FULLFSYNC), and require a fallback to
+    // fsync().
+    if (::fcntl(fd, F_FULLFSYNC) == 0) {
+      return Status::OK();
+    }
+#endif  // HAVE_FULLFSYNC
+
+#if HAVE_FDATASYNC
+    bool sync_success = ::fdatasync(fd) == 0;
+#else
+    bool sync_success = ::fsync(fd) == 0;
+#endif  // HAVE_FDATASYNC
+
+    if (sync_success) {
+      return Status::OK();
+    }
+    return PosixError(fd_path, errno);
+  }
+
   // Returns the directory name in a path pointing to a file.
   //
   // Returns "." if the path does not contain any directory separator.