diff -urN vim74_orig/src/option.c vim74/src/option.c

--- vim74_orig/src/option.c	2016-12-12 12:18:52.614342651 +0100

+++ vim74/src/option.c	2016-12-12 12:34:08.192983990 +0100

@@ -5663,6 +5663,21 @@

     return r;

 }

+ /*

+ * Return TRUE if "val" is a valid 'filetype' name.

+ * Also used for 'syntax' and 'keymap'.

+ */

+    static int

+valid_filetype(char_u *val)

+{

+    char_u *s;

+

+    for (s = val; *s != NUL; ++s)

+   if (!ASCII_ISALNUM(*s) && vim_strchr((char_u *)".-_", *s) == NULL)

+       return FALSE;

+    return TRUE;

+}

+

 /*

  * Handle string options that need some action to perform when changed.

  * Returns NULL for success, or an error message for an error.

@@ -6054,8 +6069,11 @@

 #ifdef FEAT_KEYMAP

     else if (varp == &curbuf->b_p_keymap)

     {

-	/* load or unload key mapping tables */

-	errmsg = keymap_init();

+        if (!valid_filetype(*varp))

+            errmsg = e_invarg;

+        else

+            /* load or unload key mapping tables */

+            errmsg = keymap_init();	

 	if (errmsg == NULL)

 	{

@@ -7010,6 +7028,23 @@

     }

 #endif

+#ifdef FEAT_AUTOCMD

+    else if (gvarp == &p_ft)

+    {

+   if (!valid_filetype(*varp))

+       errmsg = e_invarg;

+    }

+#endif

+

+#ifdef FEAT_SYN_HL

+    else if (gvarp == &p_syn)

+    {

+   if (!valid_filetype(*varp))

+       errmsg = e_invarg;

+    }

+#endif

+

+

     /* Options that are a list of flags. */

     else

     {