diff --git a/Makefile b/Makefile
index d628f7d..1887846 100644
--- a/Makefile
+++ b/Makefile
@@ -196,6 +196,12 @@
 $(call mark_unsupported,$(DEPENDS_ON_LIBUSB1) $(DEPENDS_ON_LIBFTDI) $(DEPENDS_ON_LIBJAYLINK))
 endif
 
+ifeq ($(TARGET_OS), $(filter $(TARGET_OS), MinGW Cygwin))
+FEATURE_CFLAGS += -D'IS_WINDOWS=1'
+else
+FEATURE_CFLAGS += -D'IS_WINDOWS=0'
+endif
+
 # FIXME: Should we check for Cygwin/MSVC as well?
 ifeq ($(TARGET_OS), MinGW)
 EXEC_SUFFIX := .exe