diff --git a/src/syntax.c b/src/syntax.c
index ccdb203..6025889 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -6316,9 +6316,11 @@
 #ifdef FEAT_SPELL
 	// TODO: keep the spell checking as it was.
 	curwin->w_p_spell = FALSE;	// No spell checking
+	// make sure option values are "empty_option" instead of NULL
 	clear_string_option(&curwin->w_s->b_p_spc);
 	clear_string_option(&curwin->w_s->b_p_spf);
 	clear_string_option(&curwin->w_s->b_p_spl);
+	clear_string_option(&curwin->w_s->b_p_spo);
 #endif
 	clear_string_option(&curwin->w_s->b_syn_isk);
     }
diff --git a/src/testdir/test_syntax.vim b/src/testdir/test_syntax.vim
index cd06892..8a02185 100644
--- a/src/testdir/test_syntax.vim
+++ b/src/testdir/test_syntax.vim
@@ -428,7 +428,11 @@
   call setline(1, '#define FOO')
   syntax on
   set filetype=c
+
   ownsyntax perl
+  " this should not crash
+  set
+
   call assert_equal('perlComment', synIDattr(synID(line('.'), col('.'), 1), 'name'))
   call assert_equal('c',    b:current_syntax)
   call assert_equal('perl', w:current_syntax)
diff --git a/src/version.c b/src/version.c
index 0d0ea4d..a59b82d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1678,
+/**/
     1677,
 /**/
     1676,