diff --git a/src/main/java/de/tlc4b/TLC4B.java b/src/main/java/de/tlc4b/TLC4B.java
index 81125adf95b5bd5e35fab7b4c696b14fe2d56a59..dcd72ea77eb42cecedfbc8acd40e9e8f58a0850a 100644
--- a/src/main/java/de/tlc4b/TLC4B.java
+++ b/src/main/java/de/tlc4b/TLC4B.java
@@ -376,7 +376,8 @@ public class TLC4B {
 		// the following lines fix incorrect file names
 		filename = filename.replace("\\", File.separator);
 		filename = filename.replace("/", File.separator);
-		if (!filename.toLowerCase().endsWith(".mch")) {
+		if (!filename.toLowerCase().endsWith(".mch") ||
+		    !filename.toLowerCase().endsWith(".sys")) {
 			filename = filename + ".mch";
 		}