diff --git a/dll/steam_remote_storage.h b/dll/steam_remote_storage.h
index d0c7646..2840abb 100644
--- a/dll/steam_remote_storage.h
+++ b/dll/steam_remote_storage.h
@@ -84,6 +84,11 @@ bool	FileWrite( const char *pchFile, const void *pvData, int32 cubData )
 {
     PRINT_DEBUG("Steam_Remote_Storage::FileWrite %s %u\n", pchFile, cubData);
     std::lock_guard<std::recursive_mutex> lock(global_mutex);
+
+    if (!pvData || cubData < 0 || cubData > k_unMaxCloudFileChunkSize) {
+        return false;
+    }
+
     int data_stored = local_storage->store_data(REMOTE_STORAGE_FOLDER, pchFile, (char* )pvData, cubData);
     PRINT_DEBUG("Steam_Remote_Storage::Stored %i, %u\n", data_stored, data_stored == cubData);
     return data_stored == cubData;
@@ -104,9 +109,15 @@ SteamAPICall_t FileWriteAsync( const char *pchFile, const void *pvData, uint32 c
 {
     PRINT_DEBUG("Steam_Remote_Storage::FileWriteAsync\n");
     std::lock_guard<std::recursive_mutex> lock(global_mutex);
+
+    if (!pvData || cubData > k_unMaxCloudFileChunkSize) {
+        return k_uAPICallInvalid;
+    }
+
     bool success = local_storage->store_data(REMOTE_STORAGE_FOLDER, pchFile, (char* )pvData, cubData) == cubData;
+
     RemoteStorageFileWriteAsyncComplete_t data;
-    data.m_eResult = k_EResultOK;
+    data.m_eResult = success ? k_EResultOK : k_EResultFail;
 
     return callback_results->addCallResult(data.k_iCallback, &data, sizeof(data));
 }