diff --git a/tccpp.c b/tccpp.c
index 4d9430d..b26dbee 100644
--- a/tccpp.c
+++ b/tccpp.c
@@ -1478,6 +1478,8 @@ static void pragma_parse(TCCState *s1)
             }
             next();
             skip(')');
+    } else if (tok == TOK_once) {
+        add_cached_include(s1, file->filename, TOK_once);
     } else {
         tcc_warning("unknown #pragma %s", get_tok_str(tok, &tokc));
     }
@@ -1618,7 +1620,7 @@ ST_FUNC void preprocess(int is_bof)
                     }
 
             e = search_cached_include(s1, buf1);
-            if (e && define_find(e->ifndef_macro)) {
+            if (e && (define_find(e->ifndef_macro) || e->ifndef_macro == TOK_once)) {
                 /* no need to parse the include because the 'ifndef macro'
                    is defined */
 #ifdef INC_DEBUG
diff --git a/tcctok.h b/tcctok.h
index ace81dc..3de3ae2 100644
--- a/tcctok.h
+++ b/tcctok.h
@@ -157,6 +157,7 @@
      DEF(TOK_lib, "lib")
      DEF(TOK_push_macro, "push_macro")
      DEF(TOK_pop_macro, "pop_macro")
+     DEF(TOK_once, "once")
 
 /* builtin functions or variables */
 #ifndef TCC_ARM_EABI