diff --git a/Generators/GBX.NET.Generators/Utils/ClassIdParser.cs b/Generators/GBX.NET.Generators/Utils/ClassIdParser.cs
index aa06feeeb..6d2454088 100644
--- a/Generators/GBX.NET.Generators/Utils/ClassIdParser.cs
+++ b/Generators/GBX.NET.Generators/Utils/ClassIdParser.cs
@@ -67,7 +67,14 @@ public static Dictionary<uint, string> Parse(TextReader reader)
                 // combine engine and class like EECCC000
                 var classId = (uint)((currentEngineByte << 24) | (classPart << 12));
 
-                result.Add(classId, currentClassName);
+                if (!result.TryGetValue(classId, out var curName) || string.IsNullOrEmpty(curName))
+                {
+                    result[classId] = currentClassName;
+                }
+                else
+                {
+                    throw new Exception($"Duplicate class id {classId:X8} with names '{curName}' and '{currentClassName}'.");
+                }
             }
             else
             {
diff --git a/Resources/ClassIdManual.txt b/Resources/ClassIdManual.txt
index 4e0cdf676..233e1b255 100644
Binary files a/Resources/ClassIdManual.txt and b/Resources/ClassIdManual.txt differ