diff --git a/tccgen.c b/tccgen.c
index ce0bdb50..1d74f6f4 100644
--- a/tccgen.c
+++ b/tccgen.c
@@ -4829,6 +4829,7 @@ ST_FUNC void unary(void)
     case TOK_SIZEOF:
     case TOK_ALIGNOF1:
     case TOK_ALIGNOF2:
+    case TOK_ALIGNOF3:
         t = tok;
         next();
         in_sizeof++;
diff --git a/tcctok.h b/tcctok.h
index b886a94d..aa29acbe 100644
--- a/tcctok.h
+++ b/tcctok.h
@@ -53,6 +53,7 @@
      DEF(TOK_ATTRIBUTE2, "__attribute__")
      DEF(TOK_ALIGNOF1, "__alignof")
      DEF(TOK_ALIGNOF2, "__alignof__")
+     DEF(TOK_ALIGNOF3, "_Alignof")
      DEF(TOK_TYPEOF1, "typeof")
      DEF(TOK_TYPEOF2, "__typeof")
      DEF(TOK_TYPEOF3, "__typeof__")