diff --git a/src/MoonSharp.Interpreter/TtsDebugger.cs b/src/MoonSharp.Interpreter/TtsDebugger.cs
index fd52e2ad..1ec25382 100644
--- a/src/MoonSharp.Interpreter/TtsDebugger.cs
+++ b/src/MoonSharp.Interpreter/TtsDebugger.cs
@@ -215,7 +215,13 @@ public static void OnStringDone(Script script)
 
 		private static string SourceCodeToTempPath(SourceCode sourceCode)
 		{
-			var scriptName = scriptNames[sourceCode.OwnerScript];
+			string scriptName;
+
+			if (!scriptNames.TryGetValue(sourceCode.OwnerScript, out scriptName))
+			{
+				scriptName = "unknown";
+			}
+
 			var sourceName = (scriptName == sourceCode.Name ? scriptName : $"{scriptName}_{sourceCode.Name}").Replace(Path.DirectorySeparatorChar, '_');
 
 			var path = Path.Combine(tempPath, sourceName + ".ttslua");