diff --git a/source/ps/tests/test_CStr.h b/source/ps/tests/test_CStr.h
index 317f8e62f4..4e7562ec20 100644
--- a/source/ps/tests/test_CStr.h
+++ b/source/ps/tests/test_CStr.h
@@ -113,8 +113,7 @@ public:
 		// 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, NULL);
-		setlocale(LC_NUMERIC, "fr_FR.UTF-8");
+		char* old = setlocale(LC_NUMERIC, "fr_FR.UTF-8");
 
 		CStr8 str1("1.234");
 		TS_ASSERT_DELTA(str1.ToFloat(), 1.234f, 0.0001f);
diff --git a/source/ps/tests/test_cppformat.h b/source/ps/tests/test_cppformat.h
index 02d0193694..df2e2f8380 100644
--- a/source/ps/tests/test_cppformat.h
+++ b/source/ps/tests/test_cppformat.h
@@ -24,6 +24,9 @@ class TestCppformat : public CxxTest::TestSuite
 public:
 	void test_basic()
 	{
+		// Make test behave independent of current host locale
+		char* old = setlocale(LC_ALL, "en_US.UTF-8");
+
 		TS_ASSERT_EQUALS(fmt::sprintf("abc"), "abc");
 
 		TS_ASSERT_EQUALS(fmt::sprintf("%d", 123), "123");
@@ -54,5 +57,7 @@ public:
 		TS_ASSERT_EQUALS(fmt::sprintf("T%sT", (const char*)NULL), "T(null)T");
 
 		TS_ASSERT_EQUALS(fmt::sprintf("T%pT", (void*)0x1234), "T0x1234T");
+
+		setlocale(LC_ALL, old);
 	}
 };