diff --git a/src/testdir/crash/double_free b/src/testdir/crash/double_free
new file mode 100644
index 0000000..895c4a0
--- /dev/null
+++ b/src/testdir/crash/double_free
Binary files differ
diff --git a/src/testdir/test_crash.vim b/src/testdir/test_crash.vim
index fd786e5..29061aa 100644
--- a/src/testdir/test_crash.vim
+++ b/src/testdir/test_crash.vim
@@ -190,6 +190,12 @@
   call term_sendkeys(buf, args)
   call TermWait(buf, 150)
 
+  let file = 'crash/double_free'
+  let cmn_args = "%s -u NONE -i NONE -n -e -s -S %s -c ':qa!'\<cr>"
+  let args = printf(cmn_args, vim, file)
+  call term_sendkeys(buf, args)
+  call TermWait(buf, 50)
+
   " clean up
   exe buf .. "bw!"
   bw!
diff --git a/src/version.c b/src/version.c
index 4dc9948..0e49ebd 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    647,
+/**/
     646,
 /**/
     645,
diff --git a/src/window.c b/src/window.c
index 7ca29d4..70c72bc 100644
--- a/src/window.c
+++ b/src/window.c
@@ -5837,10 +5837,7 @@
     win_free_lsize(wp);
 
     for (i = 0; i < wp->w_tagstacklen; ++i)
-    {
-	vim_free(wp->w_tagstack[i].tagname);
-	vim_free(wp->w_tagstack[i].user_data);
-    }
+	tagstack_clear_entry(&wp->w_tagstack[i]);
     vim_free(wp->w_localdir);
     vim_free(wp->w_prevdir);