diff --git a/Makefile b/Makefile
--- a/Makefile
+++ b/Makefile
@@ -5,7 +5,14 @@
 # % make PREFIX=/opt/ install
 
 export PREFIX=/usr/local
-PYTHON?=python
+
+# There is no python3.exe on Windows. So use the py.exe wrapper.
+ifeq($(OS),Windows_NT)
+PYTHON?=py -3
+else
+PYTHON?=python3
+endif
+
 $(eval HGROOT := $(shell pwd))
 HGPYTHONS ?= $(HGROOT)/build/pythons
 PURE=