diff --git a/src/ex_cmds.c b/src/ex_cmds.c
index 4f1d93244f021..566ed7dad32d0 100644
--- a/src/ex_cmds.c
+++ b/src/ex_cmds.c
@@ -4519,6 +4519,9 @@ ex_substitute(exarg_T *eap)
 		{
 		    nmatch = curbuf->b_ml.ml_line_count - sub_firstlnum + 1;
 		    skip_match = TRUE;
+		    // safety check
+		    if (nmatch < 0)
+			goto skip;
 		}
 
 		// Need room for:
diff --git a/src/testdir/crash/vim_regsub_both_poc b/src/testdir/crash/vim_regsub_both_poc
new file mode 100644
index 0000000000000..19a57114be60c
Binary files /dev/null and b/src/testdir/crash/vim_regsub_both_poc differ
diff --git a/src/testdir/test_crash.vim b/src/testdir/test_crash.vim
index e0884e5a058ee..f7b528c3e98d7 100644
--- a/src/testdir/test_crash.vim
+++ b/src/testdir/test_crash.vim
@@ -46,6 +46,7 @@ func Test_crash1()
 
   let file = 'crash/poc_tagfunc.vim'
   let args = printf(cmn_args, vim, file)
+  " using || because this poc causes vim to exit with exitstatus != 0
   call term_sendkeys(buf, args ..
     \ '  || echo "crash 5: [OK]" >> X_crash1_result.txt' .. "\<cr>")
 
@@ -59,6 +60,13 @@ func Test_crash1()
   call delete('X')
   call TermWait(buf, 3000)
 
+  let file = 'crash/vim_regsub_both_poc'
+  let args = printf(cmn_args, vim, file)
+  " using || because this poc causes vim to exit with exitstatus != 0
+  call term_sendkeys(buf, args ..
+    \ '  && echo "crash 7: [OK]" >> X_crash1_result.txt' .. "\<cr>")
+  call TermWait(buf, 1000)
+
   " clean up
   exe buf .. "bw!"
 
@@ -71,6 +79,7 @@ func Test_crash1()
       \ 'crash 4: [OK]',
       \ 'crash 5: [OK]',
       \ 'crash 6: [OK]',
+      \ 'crash 7: [OK]',
       \ ]
 
   call assert_equal(expected, getline(1, '$'))
diff --git a/src/version.c b/src/version.c
index a5e570e9314fd..2faa9e668ec6f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1873,
 /**/
     1872,
 /**/
diff --git a/src/window.c b/src/window.c
index 1af2395df8b91..f77ede330d304 100644
--- a/src/window.c
+++ b/src/window.c
@@ -1733,6 +1733,11 @@ win_exchange(long Prenum)
 	beep_flush();
 	return;
     }
+    if (text_or_buf_locked())
+    {
+	beep_flush();
+	return;
+    }
 
 #ifdef FEAT_GUI
     need_mouse_correct = TRUE;