3 files changed, 10 insertions, 1 deletions
diff --git a/gcc/c-family/c-opts.cc b/gcc/c-family/c-opts.cc
index 1cf119a..9833e50 100644
--- a/gcc/c-family/c-opts.cc
+++ b/gcc/c-family/c-opts.cc
@@ -1062,6 +1062,7 @@ c_common_post_options (const char **pfilename)
   /* char8_t support is implicitly enabled in C++20 and C2X.  */
   if (flag_char8_t == -1)
     flag_char8_t = (cxx_dialect >= cxx20) || flag_isoc2x;
+  cpp_opts->unsigned_utf8char = flag_char8_t ? 1 : cpp_opts->unsigned_char;
 
   if (flag_extern_tls_init)
     {
diff --git a/gcc/testsuite/g++.dg/ext/char8_t-char-literal-1.C b/gcc/testsuite/g++.dg/ext/char8_t-char-literal-1.C
index 8ed85cc..2994dd3 100644
--- a/gcc/testsuite/g++.dg/ext/char8_t-char-literal-1.C
+++ b/gcc/testsuite/g++.dg/ext/char8_t-char-literal-1.C
@@ -1,6 +1,6 @@
 // Test that UTF-8 character literals have type char if -fchar8_t is not enabled.
 // { dg-do compile }
-// { dg-options "-std=c++17 -fno-char8_t" }
+// { dg-options "-std=c++17 -fsigned-char -fno-char8_t" }
 
 template<typename T1, typename T2>
   struct is_same
@@ -10,3 +10,7 @@ template<typename T>
   { static const bool value = true; };
 
 static_assert(is_same<decltype(u8'x'), char>::value, "Error");
+
+#if u8'\0' - 1 > 0
+#error "UTF-8 character literals not signed in preprocessor"
+#endif
diff --git a/gcc/testsuite/g++.dg/ext/char8_t-char-literal-2.C b/gcc/testsuite/g++.dg/ext/char8_t-char-literal-2.C
index 7861736..db4fe70 100644
--- a/gcc/testsuite/g++.dg/ext/char8_t-char-literal-2.C
+++ b/gcc/testsuite/g++.dg/ext/char8_t-char-literal-2.C
@@ -10,3 +10,7 @@ template<typename T>
   { static const bool value = true; };
 
 static_assert(is_same<decltype(u8'x'), char8_t>::value, "Error");
+
+#if u8'\0' - 1 < 0
+#error "UTF-8 character literals not unsigned in preprocessor"
+#endif