diff --git a/src/parse/arg_matcher.rs b/src/parse/arg_matcher.rs
index 58a94059c46f..7029cdcfaeb1 100644
--- a/src/parse/arg_matcher.rs
+++ b/src/parse/arg_matcher.rs
@@ -25,6 +25,12 @@ impl ArgMatcher {
             },
             #[cfg(debug_assertions)]
             valid_subcommands: _app.subcommands.iter().map(|sc| sc.id.clone()).collect(),
+            // HACK: Allow an external subcommand's ArgMatches be a stand-in for any ArgMatches
+            // since users can't detect it and avoid the asserts.
+            //
+            // See clap-rs/clap#3263
+            #[cfg(debug_assertions)]
+            disable_asserts: _app.is_set(clap::AppSettings::AllowExternalSubcommands),
             ..Default::default()
         })
     }
diff --git a/src/parse/matches/arg_matches.rs b/src/parse/matches/arg_matches.rs
index 91a5841cae2c..cc6c87812639 100644
--- a/src/parse/matches/arg_matches.rs
+++ b/src/parse/matches/arg_matches.rs
@@ -73,6 +73,8 @@ pub struct ArgMatches {
     pub(crate) valid_args: Vec<Id>,
     #[cfg(debug_assertions)]
     pub(crate) valid_subcommands: Vec<Id>,
+    #[cfg(debug_assertions)]
+    pub(crate) disable_asserts: bool,
     pub(crate) args: IndexMap<Id, MatchedArg>,
     pub(crate) subcommand: Option<Box<SubCommand>>,
 }
@@ -1005,7 +1007,7 @@ impl ArgMatches {
         #[cfg(debug_assertions)]
         {
             let id = Id::from(_id);
-            id == Id::empty_hash() || self.valid_args.contains(&id)
+            self.disable_asserts || id == Id::empty_hash() || self.valid_args.contains(&id)
         }
         #[cfg(not(debug_assertions))]
         {
@@ -1024,7 +1026,7 @@ impl ArgMatches {
         #[cfg(debug_assertions)]
         {
             let id = Id::from(_id);
-            id == Id::empty_hash() || self.valid_subcommands.contains(&id)
+            self.disable_asserts || id == Id::empty_hash() || self.valid_subcommands.contains(&id)
         }
         #[cfg(not(debug_assertions))]
         {
@@ -1040,7 +1042,7 @@ impl ArgMatches {
     fn get_arg(&self, arg: &Id) -> Option<&MatchedArg> {
         #[cfg(debug_assertions)]
         {
-            if *arg == Id::empty_hash() || self.valid_args.contains(arg) {
+            if self.disable_asserts || *arg == Id::empty_hash() || self.valid_args.contains(arg) {
             } else if self.valid_subcommands.contains(arg) {
                 panic!(
                     "Subcommand `{:?}` used where an argument or group name was expected.",
@@ -1064,7 +1066,10 @@ impl ArgMatches {
     fn get_subcommand(&self, id: &Id) -> Option<&SubCommand> {
         #[cfg(debug_assertions)]
         {
-            if *id == Id::empty_hash() || self.valid_subcommands.contains(id) {
+            if self.disable_asserts
+                || *id == Id::empty_hash()
+                || self.valid_subcommands.contains(id)
+            {
             } else if self.valid_args.contains(id) {
                 panic!(
                     "Argument or group `{:?}` used where a subcommand name was expected.",