diff --git a/openttd.dsp b/openttd.dsp
index 7b6efc9a08..7de5b42f9e 100644
--- a/openttd.dsp
+++ b/openttd.dsp
@@ -170,6 +170,10 @@ SOURCE=.\map.c
 SOURCE=.\md5.c
 # End Source File
 
+# Begin Source File
+SOURCE=.\mersenne.c
+# End Source File
+
 # Begin Source File
 SOURCE=.\minilzo.c