--- a/src/spellfile.c
+++ b/src/spellfile.c
@@ -6125,28 +6125,31 @@ spell_message(spellinfo_T *spin, char_u 
 
 /*
  * ":[count]spellgood  {word}"
- * ":[count]spellwrong  {word}"
+ * ":[count]spellwrong {word}"
  * ":[count]spellundo  {word}"
+ * ":[count]spellrare  {word}"
  */
     void
 ex_spell(exarg_T *eap)
 {
-    spell_add_word(eap->arg, (int)STRLEN(eap->arg), eap->cmdidx == CMD_spellwrong,
+    spell_add_word(eap->arg, (int)STRLEN(eap->arg),
+		eap->cmdidx == CMD_spellwrong ? SPELL_ADD_BAD :
+		eap->cmdidx == CMD_spellrare ? SPELL_ADD_RARE : SPELL_ADD_GOOD,
 				   eap->forceit ? 0 : (int)eap->line2,
 				   eap->cmdidx == CMD_spellundo);
 }
 
 /*
- * Add "word[len]" to 'spellfile' as a good or bad word.
+ * Add "word[len]" to 'spellfile' as a good, rare or bad word.
  */
     void
 spell_add_word(
     char_u	*word,
     int		len,
-    int		bad,
-    int		idx,	    /* "zG" and "zW": zero, otherwise index in
-			       'spellfile' */
-    int		undo)	    /* TRUE for "zug", "zuG", "zuw" and "zuW" */
+    int		what,	    // SPELL_ADD_ values
+    int		idx,	    // "zG" and "zW": zero, otherwise index in
+			    // 'spellfile'
+    int		undo)	    // TRUE for "zug", "zuG", "zuw" and "zuW"
 {
     FILE	*fd = NULL;
     buf_T	*buf = NULL;
@@ -6213,7 +6216,7 @@ spell_add_word(
 	fname = fnamebuf;
     }
 
-    if (bad || undo)
+    if (what == SPELL_ADD_BAD || undo)
     {
 	/* When the word appears as good word we need to remove that one,
 	 * since its flags sort before the one with WF_BANNED. */
@@ -6280,8 +6283,10 @@ spell_add_word(
 	    semsg(_(e_notopen), fname);
 	else
 	{
-	    if (bad)
+	    if (what == SPELL_ADD_BAD)
 		fprintf(fd, "%.*s/!\n", len, word);
+	    else if (what == SPELL_ADD_RARE)
+		fprintf(fd, "%.*s/?\n", len, word);
 	    else
 		fprintf(fd, "%.*s\n", len, word);
 	    fclose(fd);