diff --git a/clang/lib/Lex/LiteralSupport.cpp b/clang/lib/Lex/LiteralSupport.cpp
--- a/clang/lib/Lex/LiteralSupport.cpp
+++ b/clang/lib/Lex/LiteralSupport.cpp
@@ -263,7 +263,8 @@
         ThisTokBuf++;
         continue;
       }
-      if (ResultChar & 0x020000000)
+      // Check if one of the top three bits is set before shifting them out.
+      if (ResultChar & 0xE0000000)
         Overflow = true;
 
       ResultChar <<= 3;
diff --git a/clang/test/Lexer/char-escapes-delimited.c b/clang/test/Lexer/char-escapes-delimited.c
--- a/clang/test/Lexer/char-escapes-delimited.c
+++ b/clang/test/Lexer/char-escapes-delimited.c
@@ -58,6 +58,8 @@
 #if __WCHAR_MAX__ > 0xFFFF
   unsigned d = L'\o{37777777777}'; // ext-warning {{extension}} cxx2b-warning {{C++2b}}
   unsigned e = L'\o{40000000000}'; // expected-error {{octal escape sequence out of range}}
+  unsigned f = L'\o{100000000000}'; // expected-error {{octal escape sequence out of range}}
+  unsigned g = L'\o{200000000000}'; // expected-error {{octal escape sequence out of range}}
 #else
   unsigned d = L'\o{177777}'; // ext-warning {{extension}} cxx2b-warning {{C++2b}}
   unsigned e = L'\o{200000}'; // expected-error {{octal escape sequence out of range}}