diff --git a/libcxx/test/support/make_string.h b/libcxx/test/support/make_string.h
--- a/libcxx/test/support/make_string.h
+++ b/libcxx/test/support/make_string.h
@@ -39,13 +39,13 @@
   const char16_t* u16;
   const char32_t* u32;
 
-  operator const char*() const { return s; }
-  operator const wchar_t*() const { return w; }
+  constexpr operator const char*() const { return s; }
+  constexpr operator const wchar_t*() const { return w; }
 #if TEST_STD_VER > 17 && defined(__cpp_char8_t)
-  operator const char8_t*() const { return u8; }
+  constexpr operator const char8_t*() const { return u8; }
 #endif
-  operator const char16_t*() const { return u16; }
-  operator const char32_t*() const { return u32; }
+  constexpr operator const char16_t*() const { return u16; }
+  constexpr operator const char32_t*() const { return u32; }
 };
 
 // Helper to convert a const char* string to a basic_string<CharT>.
@@ -56,4 +56,10 @@
     static_cast<const CharT*>(MultiStringType MKSTR(Str))                      \
   }
 
+// Helper to convert a const char* string to a const CharT*.
+// This helper is used in unit tests to make them generic. The input should be
+// valid ASCII which means the input is also valid UTF-8.
+#define MAKE_CSTRING(CharT, Str)                                               \
+  static_cast<const CharT*>(MultiStringType MKSTR(Str))
+
 #endif