diff --git a/src/spellfile.c b/src/spellfile.c
index 4a0de52..8120d75 100644
--- a/src/spellfile.c
+++ b/src/spellfile.c
@@ -4371,13 +4371,13 @@
  * Control characters and trailing '/' are invalid.  Space is OK.
  */
     static int
-valid_spell_word(char_u *word)
+valid_spell_word(char_u *word, char_u *end)
 {
     char_u *p;
 
-    if (enc_utf8 && !utf_valid_string(word, NULL))
+    if (enc_utf8 && !utf_valid_string(word, end))
 	return FALSE;
-    for (p = word; *p != NUL; p += mb_ptr2len(p))
+    for (p = word; *p != NUL && p < end; p += mb_ptr2len(p))
 	if (*p < ' ' || (p[0] == '/' && p[1] == NUL))
 	    return FALSE;
     return TRUE;
@@ -4408,7 +4408,7 @@
     char_u	*p;
 
     // Avoid adding illegal bytes to the word tree.
-    if (!valid_spell_word(word))
+    if (!valid_spell_word(word, word + len))
 	return FAIL;
 
     (void)spell_casefold(curwin, word, len, foldword, MAXWLEN);
@@ -6211,7 +6211,7 @@
     int		i;
     char_u	*spf;
 
-    if (!valid_spell_word(word))
+    if (!valid_spell_word(word, word + len))
     {
 	emsg(_(e_illegal_character_in_word));
 	return;
diff --git a/src/testdir/test_spell.vim b/src/testdir/test_spell.vim
index a291eb5..94ea3d7 100644
--- a/src/testdir/test_spell.vim
+++ b/src/testdir/test_spell.vim
@@ -884,6 +884,16 @@
   bwipe!
 endfunc
 
+func Test_spell_good_word_slash()
+  " This caused E1280.
+  new
+  norm afoo /
+  1
+  norm zG
+
+  bwipe!
+endfunc
+
 func LoadAffAndDic(aff_contents, dic_contents)
   set enc=latin1
   set spellfile=
diff --git a/src/version.c b/src/version.c
index a6a80b6..3c4e96c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -736,6 +736,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    52,
+/**/
     51,
 /**/
     50,