diff --git a/libcxx/include/__string b/libcxx/include/__string
--- a/libcxx/include/__string
+++ b/libcxx/include/__string
@@ -337,8 +337,21 @@
 
     static _LIBCPP_CONSTEXPR_AFTER_CXX14
     int compare(const char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT;
-    static inline size_t _LIBCPP_CONSTEXPR_AFTER_CXX14
-    length(const char_type* __s)  _NOEXCEPT {return __builtin_strlen(__s);}
+
+    static inline size_t _LIBCPP_CONSTEXPR_AFTER_CXX14 length(const char_type* __s)  _NOEXCEPT {
+      // GCC currently does not support __builtin_strlen during constant evaluation.
+      // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70816
+#ifdef _LIBCPP_COMPILER_GCC
+      if (__libcpp_is_constant_evaluated()) {
+        size_t __i = 0;
+        for (; __s[__i] != char_type('\0'); ++__i)
+            ;
+        return __i;
+      }
+#endif
+      return __builtin_strlen(__s);
+    }
+
     static _LIBCPP_CONSTEXPR_AFTER_CXX14
     const char_type* find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT;
     static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
diff --git a/libcxx/test/std/strings/string.view/string.view.ops/copy.pass.cpp b/libcxx/test/std/strings/string.view/string.view.ops/copy.pass.cpp
--- a/libcxx/test/std/strings/string.view/string.view.ops/copy.pass.cpp
+++ b/libcxx/test/std/strings/string.view/string.view.ops/copy.pass.cpp
@@ -6,9 +6,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-// GCC's __builtin_strlen isn't constexpr yet
-// XFAIL: gcc-11 && !(c++11 || c++14 || c++17)
-
 // <string_view>
 
 // size_type copy(charT* s, size_type n, size_type pos = 0) const;