diff --git a/libraries/libstratosphere/include/stratosphere/fs/fsa/fs_ifile.hpp b/libraries/libstratosphere/include/stratosphere/fs/fsa/fs_ifile.hpp
index 5466dfe80..422240110 100644
--- a/libraries/libstratosphere/include/stratosphere/fs/fsa/fs_ifile.hpp
+++ b/libraries/libstratosphere/include/stratosphere/fs/fsa/fs_ifile.hpp
@@ -85,7 +85,7 @@ namespace ams::fs::fsa {
         protected:
             Result DryRead(size_t *out, s64 offset, size_t size, const fs::ReadOption &option, OpenMode open_mode) {
                 /* Check that we can read. */
-                R_UNLESS((open_mode & OpenMode_Read) != 0, fs::ResultInvalidOperationForOpenMode());
+                R_UNLESS((open_mode & OpenMode_Read) != 0, fs::ResultReadNotPermitted());
 
                 /* Get the file size, and validate our offset. */
                 s64 file_size = 0;
@@ -98,12 +98,31 @@ namespace ams::fs::fsa {
 
             Result DrySetSize(s64 size, fs::OpenMode open_mode) {
                 /* Check that we can write. */
-                R_UNLESS((open_mode & OpenMode_Write) != 0, fs::ResultInvalidOperationForOpenMode());
+                R_UNLESS((open_mode & OpenMode_Write) != 0, fs::ResultWriteNotPermitted());
 
                 AMS_ASSERT(size >= 0);
 
                 return ResultSuccess();
             }
+
+            Result DryWrite(bool *out_append, s64 offset, size_t size, const fs::WriteOption &option, fs::OpenMode open_mode) {
+                /* Check that we can write. */
+                R_UNLESS((open_mode & OpenMode_Write) != 0, fs::ResultWriteNotPermitted());
+
+                /* Get the file size. */
+                s64 file_size = 0;
+                R_TRY(this->GetSize(&file_size));
+
+                /* Determine if we need to append. */
+                if (file_size < offset +  static_cast<s64>(size)) {
+                    R_UNLESS((open_mode & OpenMode_AllowAppend) != 0, fs::ResultFileExtensionWithoutOpenModeAllowAppend());
+                    *out_append = true;
+                } else {
+                    *out_append = false;
+                }
+
+                return ResultSuccess();
+            }
         private:
             virtual Result ReadImpl(size_t *out, s64 offset, void *buffer, size_t size, const fs::ReadOption &option) = 0;
             virtual Result GetSizeImpl(s64 *out) = 0;
diff --git a/libraries/libvapours/include/vapours/results/fs_results.hpp b/libraries/libvapours/include/vapours/results/fs_results.hpp
index eb8bde043..c2985f2e1 100644
--- a/libraries/libvapours/include/vapours/results/fs_results.hpp
+++ b/libraries/libvapours/include/vapours/results/fs_results.hpp
@@ -240,6 +240,8 @@ namespace ams::fs {
 
             R_DEFINE_ERROR_RANGE(InvalidOperationForOpenMode, 6200, 6299);
                 R_DEFINE_ERROR_RESULT(FileExtensionWithoutOpenModeAllowAppend, 6201);
+                R_DEFINE_ERROR_RESULT(ReadNotPermitted,                        6202);
+                R_DEFINE_ERROR_RESULT(WriteNotPermitted,                       6203);
 
             R_DEFINE_ERROR_RANGE(UnsupportedOperation, 6300, 6399);
                 R_DEFINE_ERROR_RESULT(UnsupportedOperationInSubStorageA,                    6302);