Index: source/ps/tests/test_CStr.h
===================================================================
--- source/ps/tests/test_CStr.h
+++ source/ps/tests/test_CStr.h
@@ -113,7 +113,8 @@
 		// because GTK+ can change the locale when we're running Atlas.
 		// (If the host system doesn't have the locale we're using for this test
 		// then it'll just stick with the default, which is fine)
-		char* old = setlocale(LC_NUMERIC, "fr_FR.UTF-8");
+		char* old = setlocale(LC_NUMERIC, NULL);
+		setlocale(LC_NUMERIC, "fr_FR.UTF-8");
 
 		CStr8 str1("1.234");
 		TS_ASSERT_DELTA(str1.ToFloat(), 1.234f, 0.0001f);
Index: source/ps/tests/test_cppformat.h
===================================================================
--- source/ps/tests/test_cppformat.h
+++ source/ps/tests/test_cppformat.h
@@ -25,7 +25,8 @@
 	void test_basic()
 	{
 		// Make test behave independent of current host locale
-		char* old = setlocale(LC_ALL, "en_US.UTF-8");
+		char* old = setlocale(LC_ALL, NULL);
+		setlocale(LC_ALL, "en_US.UTF-8");
 
 		TS_ASSERT_EQUALS(fmt::sprintf("abc"), "abc");