diff --git a/Visual Studio Projects/AltairZ80.vcproj b/Visual Studio Projects/AltairZ80.vcproj
index 832263be..790682dc 100644
--- a/Visual Studio Projects/AltairZ80.vcproj	
+++ b/Visual Studio Projects/AltairZ80.vcproj	
@@ -377,6 +377,10 @@
 				RelativePath="..\AltairZ80\s100_tarbell.c"
 				>
 			</File>
+			<File
+				RelativePath="..\AltairZ80\s100_tdd.c"
+				>
+			</File>
 			<File
 				RelativePath="..\scp.c"
 				>