diff --git a/libstdc++-v3/include/std/limits b/libstdc++-v3/include/std/limits
index 3567a328400..49ce7c935e9 100644
--- a/libstdc++-v3/include/std/limits
+++ b/libstdc++-v3/include/std/limits
@@ -2128,7 +2128,7 @@ __glibcxx_float_n(128)
       static _GLIBCXX_USE_CONSTEXPR int digits = 113;
       static _GLIBCXX_USE_CONSTEXPR int digits10 = 33;
 #if __cplusplus >= 201103L
-      static constexpr int max_digits10 = 35;
+      static constexpr int max_digits10 = 36;
 #endif
       static _GLIBCXX_USE_CONSTEXPR bool is_signed = true;
       static _GLIBCXX_USE_CONSTEXPR bool is_integer = false;
diff --git a/libstdc++-v3/testsuite/18_support/numeric_limits/128bit.cc b/libstdc++-v3/testsuite/18_support/numeric_limits/128bit.cc
index b13d83776ba..bf12b65f91a 100644
--- a/libstdc++-v3/testsuite/18_support/numeric_limits/128bit.cc
+++ b/libstdc++-v3/testsuite/18_support/numeric_limits/128bit.cc
@@ -4,6 +4,11 @@
 
 #if __SIZEOF_FLOAT128__
 __extension__ template class std::numeric_limits<__float128>;
+
+# if __cplusplus >= 201103L
+static_assert( std::numeric_limits<__float128>::max_digits10 == 36,
+	       "PR libstdc++/121374" );
+# endif
 #endif
 
 #if __SIZEOF_INT128__