diff --git a/src/openrct2/rct12/SawyerEncoding.cpp b/src/openrct2/rct12/SawyerEncoding.cpp
index d1b161010e..fa0fa45141 100644
--- a/src/openrct2/rct12/SawyerEncoding.cpp
+++ b/src/openrct2/rct12/SawyerEncoding.cpp
@@ -97,4 +97,41 @@ namespace SawyerEncoding
         }
         return success;
     }
+
+    bool ValidateChecksum(IStream * stream)
+    {
+        // Get data size
+        uint64 initialPosition = stream->GetPosition();
+        uint64 dataSize = stream->GetLength() - initialPosition;
+        if (dataSize < 8)
+        {
+            return false;
+        }
+        dataSize -= 4;
+
+        // Calculate checksum
+        uint32 checksum = 0;
+        do
+        {
+            uint8 buffer[4096];
+            uint64 bufferSize = Math::Min(dataSize, sizeof(buffer));
+            stream->Read(buffer, bufferSize);
+
+            for (uint64 i = 0; i < bufferSize; i++)
+            {
+                checksum += buffer[i];
+            }
+
+            dataSize -= bufferSize;
+        }
+        while (dataSize != 0);
+
+        // Read file checksum
+        uint32 fileChecksum = stream->ReadValue<uint32>();
+
+        // Rewind
+        stream->SetPosition(initialPosition);
+
+        return checksum == fileChecksum;
+    }
 }
diff --git a/src/openrct2/rct12/SawyerEncoding.h b/src/openrct2/rct12/SawyerEncoding.h
index ace15db533..bf25b6824b 100644
--- a/src/openrct2/rct12/SawyerEncoding.h
+++ b/src/openrct2/rct12/SawyerEncoding.h
@@ -31,4 +31,6 @@ namespace SawyerEncoding
     {
         return TryReadChunk(dst, sizeof(T), stream);
     }
+
+    bool ValidateChecksum(IStream * stream);
 }
diff --git a/src/openrct2/rct2/S6Importer.cpp b/src/openrct2/rct2/S6Importer.cpp
index 923efed6e7..8eca777a28 100644
--- a/src/openrct2/rct2/S6Importer.cpp
+++ b/src/openrct2/rct2/S6Importer.cpp
@@ -85,15 +85,6 @@ public:
 
     void LoadSavedGame(const utf8 * path) override
     {
-        // if (!sawyercoding_validate_checksum(rw))
-        // {
-        //     gErrorType = ERROR_TYPE_FILE_LOAD;
-        //     gGameCommandErrorTitle = STR_FILE_CONTAINS_INVALID_DATA;
-        // 
-        //     log_error("failed to load saved game, invalid checksum");
-        //     throw IOException("Invalid SV6 checksum.");
-        // }
-
         auto fs = FileStream(path, FILE_MODE_OPEN);
         LoadFromStream(&fs, false);
         _s6Path = path;
@@ -101,17 +92,6 @@ public:
 
     void LoadScenario(const utf8 * path) override
     {
-        // if (!gConfigGeneral.allow_loading_with_incorrect_checksum && !sawyercoding_validate_checksum(rw))
-        // {
-        //     SDL_RWclose(rw);
-        // 
-        //     gErrorType = ERROR_TYPE_FILE_LOAD;
-        //     gErrorStringId = STR_FILE_CONTAINS_INVALID_DATA;
-        // 
-        //     log_error("failed to load scenario, invalid checksum");
-        //     throw IOException("Invalid SC6 checksum.");
-        // }
-
         auto fs = FileStream(path, FILE_MODE_OPEN);
         LoadFromStream(&fs, true);
         _s6Path = path;
@@ -119,6 +99,11 @@ public:
 
     void LoadFromStream(IStream * stream, bool isScenario)
     {
+        if (!gConfigGeneral.allow_loading_with_incorrect_checksum && !SawyerEncoding::ValidateChecksum(stream))
+        {
+            throw IOException("Invalid checksum.");
+        }
+
         SawyerEncoding::ReadChunkTolerant(&_s6.header, sizeof(_s6.header), stream);
 
         log_verbose("saved game classic_flag = 0x%02x\n", _s6.header.classic_flag);