Index: clang/lib/Lex/PPExpressions.cpp
===================================================================
--- clang/lib/Lex/PPExpressions.cpp
+++ clang/lib/Lex/PPExpressions.cpp
@@ -407,10 +407,10 @@
     llvm::APSInt Val(NumBits);
     // Set the value.
     Val = Literal.getValue();
-    // Set the signedness. UTF-16 and UTF-32 are always unsigned
+    // Set the signedness. UTF-8, UTF-16 and UTF-32 are always unsigned
     if (Literal.isWide())
       Val.setIsUnsigned(!TargetInfo::isTypeSigned(TI.getWCharType()));
-    else if (!Literal.isUTF16() && !Literal.isUTF32())
+    else if (!Literal.isUTF8() && !Literal.isUTF16() && !Literal.isUTF32())
       Val.setIsUnsigned(!PP.getLangOpts().CharIsSigned);
 
     if (Result.Val.getBitWidth() > Val.getBitWidth()) {
Index: clang/test/Lexer/utf8-char-literal.cpp
===================================================================
--- clang/test/Lexer/utf8-char-literal.cpp
+++ clang/test/Lexer/utf8-char-literal.cpp
@@ -26,3 +26,10 @@
              unsigned char : 1),
     "Surprise!");
 #endif
+
+/// Test u8 char literal preprocessor behavior
+#if __cplusplus > 201402L || __STDC_VERSION__ > 202000L
+#if u8'\xff' != 0xff
+#error u8 char literal is not unsigned
+#endif
+#endif