diff --git a/SConstruct b/SConstruct
index 096b7f340..309d935c3 100644
--- a/SConstruct
+++ b/SConstruct
@@ -495,6 +495,8 @@ struct %(N)s_derived : %(N)s_base {
 """.format(macro_name=macro_name, macro_value=macro_value, test=test), **kwargs)
 		if not r:
 			macro_value = _comment_not_supported
+		self._define_macro(context, macro_name, macro_value)
+	def _define_macro(self,context,macro_name,macro_value):
 		context.sconf.Define(macro_name, macro_value)
 		self.__defined_macros += '#define %s %s\n' % (macro_name, macro_value)
 	implicit_tests.append(_implicit_test.RecordedTest('check_ccache_distcc_ld_works', "assume ccache, distcc, C++ compiler, and C++ linker work"))
@@ -1063,7 +1065,7 @@ int main(int argc,char**argv){(void)argc;(void)argv;
 		context.Display('%s: checking whether to use %s...%s\n' % (self.msgprefix, mixer, 'yes' if user_settings.sdlmixer else 'no'))
 		# SDL_mixer support?
 		use_sdlmixer = user_settings.sdlmixer
-		context.sconf.Define('DXX_USE_SDLMIXER', int(use_sdlmixer))
+		self._define_macro(context, 'DXX_USE_SDLMIXER', int(use_sdlmixer))
 		if not use_sdlmixer:
 			return
 		successflags = self.pkgconfig.merge(context, self.msgprefix, user_settings, mixer, mixer, guess_flags)
@@ -1838,6 +1840,7 @@ help:add Valgrind annotations; wipe certain freed memory when running under Valg
 		if not r:
 			return
 		text = '''
+#define DXX_HAVE_POISON	1
 #include "poison.h"
 '''
 		main = '''
@@ -1868,8 +1871,7 @@ help:always wipe certain freed memory
 		for f in _methods:
 			if f(self, context):
 				poison = True
-		if poison:
-			context.sconf.Define('DXX_HAVE_POISON')
+		self._define_macro(context, 'DXX_HAVE_POISON', int(poison))
 	implicit_tests.append(_implicit_test.RecordedTest('check_size_type_size', "assume size_t is formatted as `size_t`"))
 	implicit_tests.append(_implicit_test.RecordedTest('check_size_type_long', "assume size_t is formatted as `unsigned long`"))
 	implicit_tests.append(_implicit_test.RecordedTest('check_size_type_int', "assume size_t is formatted as `unsigned int`"))
diff --git a/common/include/physfsx.h b/common/include/physfsx.h
index 006e6ba36..f376ac310 100644
--- a/common/include/physfsx.h
+++ b/common/include/physfsx.h
@@ -238,7 +238,7 @@ struct PHYSFSX_gets_line_t
 	PHYSFSX_gets_line_t(PHYSFSX_gets_line_t &&) = default;
 	PHYSFSX_gets_line_t &operator=(PHYSFSX_gets_line_t &&) = default;
 	typedef array<char, N> line_t;
-#ifdef DXX_HAVE_POISON
+#if DXX_HAVE_POISON
 	/* Force onto heap to improve checker accuracy */
 	std::unique_ptr<line_t> m_line;
 	const line_t &line() const { return *m_line.get(); }
@@ -274,7 +274,7 @@ struct PHYSFSX_gets_line_t<0>
 	std::unique_ptr<char[]> m_line;
 	std::size_t m_length;
 	PHYSFSX_gets_line_t(std::size_t n) :
-#ifndef DXX_HAVE_POISON
+#if !DXX_HAVE_POISON
 		m_line(DXX_ALLOCATE_PHYSFS_LINE(n)),
 #endif
 		m_length(n)
@@ -284,7 +284,7 @@ struct PHYSFSX_gets_line_t<0>
 	const char *line() const { return m_line.get(); }
 	char *next()
 	{
-#ifdef DXX_HAVE_POISON
+#if DXX_HAVE_POISON
 		/* Reallocate to tell checker to undefine the buffer */
 		m_line = DXX_ALLOCATE_PHYSFS_LINE(m_length);
 #endif
diff --git a/common/include/poison.h b/common/include/poison.h
index 95034edd7..e26c1ceae 100644
--- a/common/include/poison.h
+++ b/common/include/poison.h
@@ -31,7 +31,7 @@ static inline void DXX_MAKE_VAR_UNDEFINED(T &b)
 template <typename T, typename V>
 static inline void _DXX_POISON_MEMORY_RANGE(T b, T e, const V &v)
 {
-#ifdef DXX_HAVE_POISON
+#if DXX_HAVE_POISON
 	int store = 0;
 #ifdef DXX_HAVE_POISON_OVERWRITE
 	store |= 1;
diff --git a/similar/main/bm.cpp b/similar/main/bm.cpp
index 31b42e93f..817c8b48f 100644
--- a/similar/main/bm.cpp
+++ b/similar/main/bm.cpp
@@ -735,7 +735,7 @@ void compute_average_rgb(grs_bitmap *bm, array<fix, 3> &rgb)
 		auto sbits = &bm->get_bitmap_data()[4 + (bm->bm_h * data_offset)];
 		for (uint_fast32_t i = 0; i != bm_h; ++i)
 		{
-#ifdef DXX_HAVE_POISON
+#if DXX_HAVE_POISON
 			/* Reallocate to undefine buffer */
 			buf = make_unique<uint8_t[]>(bm_w);
 #endif