diff --git a/include/rocksdb/env.h b/include/rocksdb/env.h
index 9e7d317933..d81960c437 100644
--- a/include/rocksdb/env.h
+++ b/include/rocksdb/env.h
@@ -1002,7 +1002,7 @@ class WritableFile {
   /*
    * Get the size of valid data in the file.
    */
-  virtual uint64_t GetFileSize() { return 0; }
+  virtual uint64_t GetFileSize() = 0;
 
   /*
    * Get and set the default pre-allocation block size for writes to
diff --git a/include/rocksdb/file_system.h b/include/rocksdb/file_system.h
index 08b339f2c7..fb2fc8dbb7 100644
--- a/include/rocksdb/file_system.h
+++ b/include/rocksdb/file_system.h
@@ -1144,9 +1144,7 @@ class FSWritableFile {
    * Get the size of valid data in the file.
    */
   virtual uint64_t GetFileSize(const IOOptions& /*options*/,
-                               IODebugContext* /*dbg*/) {
-    return 0;
-  }
+                               IODebugContext* /*dbg*/) = 0;
 
   /*
    * Get and set the default pre-allocation block size for writes to
diff --git a/test_util/testutil.h b/test_util/testutil.h
index c484db649e..5643c82b65 100644
--- a/test_util/testutil.h
+++ b/test_util/testutil.h
@@ -189,6 +189,11 @@ class StringSink : public FSWritableFile {
     }
   }
 
+  uint64_t GetFileSize(const IOOptions& /*options*/,
+                       IODebugContext* /*dbg*/) override {
+    return contents_.size();
+  }
+
  private:
   Slice* reader_contents_;
   size_t last_flush_;
@@ -285,6 +290,11 @@ class OverwritingStringSink : public FSWritableFile {
     if (last_flush_ > contents_.size()) last_flush_ = contents_.size();
   }
 
+  uint64_t GetFileSize(const IOOptions& /*options*/,
+                       IODebugContext* /*dbg*/) override {
+    return contents_.size();
+  }
+
  private:
   std::string contents_;
   Slice* reader_contents_;
@@ -562,6 +572,14 @@ class StringFS : public FileSystemWrapper {
       return IOStatus::OK();
     }
 
+    uint64_t GetFileSize(const IOOptions& /*options*/,
+                         IODebugContext* /*dbg*/) override {
+      if (contents_ != nullptr) {
+        return contents_->size();
+      }
+      return 0;
+    }
+
    private:
     std::string* contents_;
   };
diff --git a/unreleased_history/public_api_changes/remove_default_get_file_size.md b/unreleased_history/public_api_changes/remove_default_get_file_size.md
new file mode 100644
index 0000000000..b983a25b7f
--- /dev/null
+++ b/unreleased_history/public_api_changes/remove_default_get_file_size.md
@@ -0,0 +1 @@
+*Remove the default `WritableFile::GetFileSize` and `FSWritableFile::GetFileSize` implementation that returns 0 and make it pure virtual, so that subclasses are enforced to explicitly provide an implementation.
\ No newline at end of file
diff --git a/util/file_reader_writer_test.cc b/util/file_reader_writer_test.cc
index dfdd7d32c7..f317119e75 100644
--- a/util/file_reader_writer_test.cc
+++ b/util/file_reader_writer_test.cc
@@ -463,6 +463,11 @@ TEST_F(WritableFileWriterTest, AppendStatusReturn) {
     void Setuse_direct_io(bool val) { use_direct_io_ = val; }
     void SetIOError(bool val) { io_error_ = val; }
 
+    uint64_t GetFileSize(const IOOptions& /*options*/,
+                         IODebugContext* /*dbg*/) override {
+      return 0;
+    }
+
    protected:
     bool use_direct_io_;
     bool io_error_;
@@ -862,6 +867,11 @@ TEST_F(DBWritableFileWriterTest, IOErrorNotification) {
       ASSERT_EQ(file_flush_errors_, file_flush_errors);
     }
 
+    uint64_t GetFileSize(const IOOptions& /*options*/,
+                         IODebugContext* /*dbg*/) override {
+      return 0;
+    }
+
    protected:
     bool io_error_;
     std::atomic<size_t> file_append_errors_;
diff --git a/utilities/fault_injection_fs.h b/utilities/fault_injection_fs.h
index 45691ba1b3..6b4836d503 100644
--- a/utilities/fault_injection_fs.h
+++ b/utilities/fault_injection_fs.h
@@ -96,6 +96,11 @@ class TestFSWritableFile : public FSWritableFile {
     return target_->use_direct_io();
   }
 
+  virtual uint64_t GetFileSize(const IOOptions& options,
+                               IODebugContext* dbg) override {
+    return target_->GetFileSize(options, dbg);
+  }
+
  private:
   FSFileState state_;  // Need protection by mutex_
   FileOptions file_opts_;