Set PYTHON using ?= syntax
diff --git a/tests/Makefile b/tests/Makefile
index b3ab036..88d91ef 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -39,10 +39,13 @@
 ifdef SHARED
 SHARED_SUFFIX=.$(DLEXT)
 endif
+PYTHON ?= python
 else
 DLEXT ?= so
 EXEXT=
 SHARED_SUFFIX=
+# python2 for POSIX since FreeBSD has only python2 as default.
+PYTHON ?= python2
 endif
 
 # Zlib shared library extensions:
@@ -50,15 +53,6 @@
 LOCAL_LDFLAGS += -lz
 endif
 
-# Python executable
-ifndef PYTHON
-ifdef WINDOWS
-PYTHON=python
-else
-PYTHON=python2
-endif
-endif
-
 APPS =	test_suite_aes.ecb	test_suite_aes.cbc		\
 	test_suite_aes.cfb	test_suite_aes.ofb		\
 	test_suite_aes.xts					\