diff --git a/tools/Makefile b/tools/Makefile
index c1313a2..c191203 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -96,6 +96,7 @@
 #
 ifeq ($(HOSTOS),cygwin)
 SFX = .exe
+HOST_CFLAGS += -D__WIN32__
 else
 SFX =
 endif