diff --git a/src/map.c b/src/map.c
index eed3a55..6a994d4 100644
--- a/src/map.c
+++ b/src/map.c
@@ -2304,6 +2304,8 @@
     char_u	*arg;
 
     which = tv_get_string_buf_chk(&argvars[0], buf);
+    if (which == NULL)
+	return;
     mode = get_map_mode(&which, 0);
     is_abbr = (int)tv_get_number(&argvars[1]);
 
diff --git a/src/testdir/test_maparg.vim b/src/testdir/test_maparg.vim
index ea921d6..285474d 100644
--- a/src/testdir/test_maparg.vim
+++ b/src/testdir/test_maparg.vim
@@ -238,6 +238,8 @@
   iunmap K
   let &cpo = cpo_save
   bwipe!
+
+  call assert_fails('call mapset([], v:false, {})', 'E730:')
 endfunc
 
 func Check_ctrlb_map(d, check_alt)
diff --git a/src/version.c b/src/version.c
index d5c8f30..acac541 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1773,
+/**/
     1772,
 /**/
     1771,