diff --git a/src/insexpand.c b/src/insexpand.c
index 9b5e5de..93a56a8 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -2741,6 +2741,7 @@
     --textlock;
 
     curwin->w_cursor = pos;	// restore the cursor position
+    check_cursor();  // make sure cursor position is valid, just in case
     validate_cursor();
     if (!EQUAL_POS(curwin->w_cursor, pos))
     {
@@ -4606,6 +4607,7 @@
 
     State = save_State;
     curwin->w_cursor = pos;	// restore the cursor position
+    check_cursor();  // make sure cursor position is valid, just in case
     validate_cursor();
     if (!EQUAL_POS(curwin->w_cursor, pos))
     {
diff --git a/src/testdir/test_ins_complete.vim b/src/testdir/test_ins_complete.vim
index 376d82f..eb89a15 100644
--- a/src/testdir/test_ins_complete.vim
+++ b/src/testdir/test_ins_complete.vim
@@ -2429,4 +2429,26 @@
   call StopVimInTerminal(buf)
 endfunc
 
+func Test_completefunc_first_call_complete_add()
+  new
+
+  func Complete(findstart, base) abort
+    if a:findstart
+      let col = col('.')
+      call complete_add('#')
+      return col - 1
+    else
+      return []
+    endif
+  endfunc
+
+  set completeopt=longest completefunc=Complete
+  " This used to cause heap-buffer-overflow
+  call assert_fails('call feedkeys("ifoo#\<C-X>\<C-U>", "xt")', 'E840:')
+
+  delfunc Complete
+  set completeopt& completefunc&
+  bwipe!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab nofoldenable
diff --git a/src/version.c b/src/version.c
index 4c7ab84..abb028b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    254,
+/**/
     253,
 /**/
     252,