diff --git a/tcc.c b/tcc.c
index 6adb6b8..722bd4c 100644
--- a/tcc.c
+++ b/tcc.c
@@ -99,7 +99,7 @@ static void help(void)
            "  -Usym       undefine 'sym'\n"
            "  -E          preprocess only\n"
            "  -P[1]       no/alternative output of #line directives with -E\n"
-           "  -dD -dM     dump defines (only with -E)\n"
+           "  -d{D|M}     dump defines (only with -E)\n"
            "Linker options:\n"
            "  -Ldir       add library path 'dir'\n"
            "  -llib       link with dynamic or static library 'lib'\n"
diff --git a/tccpp.c b/tccpp.c
index f499774..58eb5f6 100644
--- a/tccpp.c
+++ b/tccpp.c
@@ -1444,6 +1444,8 @@ static inline void add_cached_include(TCCState *s1, const char *filename, int if
     s1->cached_includes_hash[h] = s1->nb_cached_includes;
 }
 
+#define ONCE_PREFIX "#ONCE#"
+
 static void pragma_parse(TCCState *s1)
 {
     next_nomacro();
@@ -1475,10 +1477,12 @@ static void pragma_parse(TCCState *s1)
             tcc_warning("unbalanced #pragma pop_macro");
 
     } else if (tok == TOK_once) {
-        char buf1[sizeof file->filename];
-
-        pstrcpy(buf1, sizeof(buf1), "#once#");
-        pstrcat(buf1, sizeof(buf1), file->filename);
+        char buf1[sizeof(file->filename) + sizeof(ONCE_PREFIX)];
+        strcpy(buf1, ONCE_PREFIX);
+        strcat(buf1, file->filename);
+#if PATHCMP==stricmp
+        strupr(buf1);
+#endif
         add_cached_include(s1, file->filename, tok_alloc(buf1, strlen(buf1))->tok);
     } else if (s1->ppfp) {
         /* tcc -E: keep pragmas below unchanged */