diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -614,7 +614,8 @@
   endif()
   target_add_compile_flags_if_supported(${target} PRIVATE -Wextra -W -Wwrite-strings
                                                           -Wno-unused-parameter -Wno-long-long
-                                                          -Werror=return-type -Wextra-semi -Wundef)
+                                                          -Werror=return-type -Wextra-semi -Wundef
+                                                          -Wformat-nonliteral)
   if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
     target_add_compile_flags_if_supported(${target} PRIVATE
       -Wno-user-defined-literals
diff --git a/libcxx/include/locale b/libcxx/include/locale
--- a/libcxx/include/locale
+++ b/libcxx/include/locale
@@ -1486,7 +1486,10 @@
         + ((numeric_limits<_Unsigned>::digits % 3) != 0) // round up
         + 2; // base prefix + terminating null character
     char __nar[__nbuf];
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wformat-nonliteral"
     int __nc = __libcpp_snprintf_l(__nar, sizeof(__nar), _LIBCPP_GET_C_LOCALE, __fmt, __v);
+#pragma clang diagnostic pop
     char* __ne = __nar + __nc;
     char* __np = this->__identify_padding(__nar, __ne, __iob);
     // Stage 2 - Widen __nar while adding thousands separators
@@ -1546,6 +1549,8 @@
     char __nar[__nbuf];
     char* __nb = __nar;
     int __nc;
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wformat-nonliteral"
     if (__specify_precision)
         __nc = __libcpp_snprintf_l(__nb, __nbuf, _LIBCPP_GET_C_LOCALE, __fmt,
                                    (int)__iob.precision(), __v);
@@ -1562,6 +1567,7 @@
             __throw_bad_alloc();
         __nbh.reset(__nb);
     }
+#pragma clang diagnostic pop
     char* __ne = __nb + __nc;
     char* __np = this->__identify_padding(__nb, __ne, __iob);
     // Stage 2 - Widen __nar while adding thousands separators
@@ -1606,10 +1612,9 @@
                                          char_type __fl, const void* __v) const
 {
     // Stage 1 - Get pointer in narrow char
-    char __fmt[6] = "%p";
     const unsigned __nbuf = 20;
     char __nar[__nbuf];
-    int __nc = __libcpp_snprintf_l(__nar, sizeof(__nar), _LIBCPP_GET_C_LOCALE, __fmt, __v);
+    int __nc = __libcpp_snprintf_l(__nar, sizeof(__nar), _LIBCPP_GET_C_LOCALE, "%p", __v);
     char* __ne = __nar + __nc;
     char* __np = this->__identify_padding(__nar, __ne, __iob);
     // Stage 2 - Widen __nar