diff --git a/src/nvim/spellfile.c b/src/nvim/spellfile.c
index f8c10d0258..41669789db 100644
--- a/src/nvim/spellfile.c
+++ b/src/nvim/spellfile.c
@@ -5095,7 +5095,8 @@ mkspell (
   spin.si_newcompID = 127;      // start compound ID at first maximum
 
   // default: fnames[0] is output file, following are input files
-  innames = &fnames[1];
+  // When "fcount" is 1 there is only one file.
+  innames = &fnames[fcount == 1 ? 0 : 1];
   incount = fcount - 1;
 
   wfname = xmalloc(MAXPATHL);
@@ -5105,12 +5106,10 @@ mkspell (
     if (fcount == 1 && len > 4 && STRCMP(fnames[0] + len - 4, ".add") == 0) {
       // For ":mkspell path/en.latin1.add" output file is
       // "path/en.latin1.add.spl".
-      innames = &fnames[0];
       incount = 1;
       vim_snprintf((char *)wfname, MAXPATHL, "%s.spl", fnames[0]);
     } else if (fcount == 1)   {
       // For ":mkspell path/vim" output file is "path/vim.latin1.spl".
-      innames = &fnames[0];
       incount = 1;
       vim_snprintf((char *)wfname, MAXPATHL, SPL_FNAME_TMPL,
           fnames[0], spin.si_ascii ? (char_u *)"ascii" : spell_enc());