3 files changed, 32 insertions, 1 deletions
diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index 67c346237c..7e0122acd2 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -1459,6 +1459,24 @@ static char_u * do_one_cmd(char_u **cmdlinep,
   /* Find the command and let "p" point to after it. */
   p = find_command(&ea, NULL);
 
+  // If this looks like an undefined user command and there are CmdUndefined
+  // autocommands defined, trigger the matching autocommands.
+  if (p != NULL && ea.cmdidx == CMD_SIZE && !ea.skip
+      && ASCII_ISUPPER(*ea.cmd)
+      && has_cmdundefined()) {
+    char_u *p = ea.cmd;
+
+    while (ASCII_ISALNUM(*p)) {
+      ++p;
+    }
+    p = vim_strnsave(ea.cmd, p - ea.cmd);
+    int ret = apply_autocmds(EVENT_CMDUNDEFINED, p, p, TRUE, NULL);
+    free(p);
+    if (ret && !aborting()) {
+      p = find_command(&ea, NULL);
+    }
+  }
+
   if (p == NULL) {
     if (!ea.skip)
       errormsg = (char_u *)_("E464: Ambiguous use of user-defined command");
diff --git a/src/nvim/fileio.c b/src/nvim/fileio.c
index 4486d43578..b20150b2c9 100644
--- a/src/nvim/fileio.c
+++ b/src/nvim/fileio.c
@@ -5198,6 +5198,7 @@ static struct event_name {
   {"BufWriteCmd",     EVENT_BUFWRITECMD},
   {"CmdwinEnter",     EVENT_CMDWINENTER},
   {"CmdwinLeave",     EVENT_CMDWINLEAVE},
+  {"CmdUndefined",    EVENT_CMDUNDEFINED},
   {"ColorScheme",     EVENT_COLORSCHEME},
   {"CompleteDone",    EVENT_COMPLETEDONE},
   {"CursorHold",      EVENT_CURSORHOLD},
@@ -6462,6 +6463,18 @@ int has_insertcharpre(void)
   return first_autopat[(int)EVENT_INSERTCHARPRE] != NULL;
 }
 
+/// @returns true when there is an CmdUndefined autocommand defined.
+int has_cmdundefined(void)
+{
+  return first_autopat[(int)EVENT_CMDUNDEFINED] != NULL;
+}
+
+/// @returns true when there is an FuncUndefined autocommand defined.
+int has_funcundefined(void)
+{
+  return first_autopat[(int)EVENT_FUNCUNDEFINED] != NULL;
+}
+
 static int 
 apply_autocmds_group (
     event_T event,
diff --git a/src/nvim/version.c b/src/nvim/version.c
index 137f85bb2b..7f80c57242 100644
--- a/src/nvim/version.c
+++ b/src/nvim/version.c
@@ -251,7 +251,7 @@ static int included_patches[] = {
   //417,
   //416,
   //415,
-  //414,
+  414,
   //413 NA
   //412 NA
   411,