diff --git a/make_helpers/cygwin.mk b/make_helpers/cygwin.mk
index f99be13..e69c0b1 100644
--- a/make_helpers/cygwin.mk
+++ b/make_helpers/cygwin.mk
@@ -37,4 +37,7 @@
 
     include ${MAKE_HELPERS_DIRECTORY}unix.mk
 
+    # In cygwin executable files have the Windows .exe extension type.
+    BIN_EXT := .exe
+
 endif