diff --git a/clap_complete/tests/common.rs b/clap_complete/tests/common.rs
index 3fd22100478..f68e3de1a75 100644
--- a/clap_complete/tests/common.rs
+++ b/clap_complete/tests/common.rs
@@ -48,7 +48,7 @@ pub fn special_commands_command(name: &'static str) -> clap::Command<'static> {
                 .about("tests other things")
                 .arg(
                     clap::Arg::new("config")
-                        .long("--config")
+                        .long("config")
                         .hide(true)
                         .takes_value(true)
                         .require_equals(true)
@@ -139,7 +139,7 @@ pub fn sub_subcommands_command(name: &'static str) -> clap::Command<'static> {
             .subcommand(
                 clap::Command::new("sub_cmd").about("sub-subcommand").arg(
                     clap::Arg::new("config")
-                        .long("--config")
+                        .long("config")
                         .takes_value(true)
                         .possible_values([clap::PossibleValue::new("Lest quotes aren't escaped.")])
                         .help("the other case to test"),
diff --git a/clap_complete_fig/tests/common.rs b/clap_complete_fig/tests/common.rs
index 3fd22100478..f68e3de1a75 100644
--- a/clap_complete_fig/tests/common.rs
+++ b/clap_complete_fig/tests/common.rs
@@ -48,7 +48,7 @@ pub fn special_commands_command(name: &'static str) -> clap::Command<'static> {
                 .about("tests other things")
                 .arg(
                     clap::Arg::new("config")
-                        .long("--config")
+                        .long("config")
                         .hide(true)
                         .takes_value(true)
                         .require_equals(true)
@@ -139,7 +139,7 @@ pub fn sub_subcommands_command(name: &'static str) -> clap::Command<'static> {
             .subcommand(
                 clap::Command::new("sub_cmd").about("sub-subcommand").arg(
                     clap::Arg::new("config")
-                        .long("--config")
+                        .long("config")
                         .takes_value(true)
                         .possible_values([clap::PossibleValue::new("Lest quotes aren't escaped.")])
                         .help("the other case to test"),
diff --git a/clap_mangen/tests/common.rs b/clap_mangen/tests/common.rs
index 27a2e951cf6..9d8ee45b166 100644
--- a/clap_mangen/tests/common.rs
+++ b/clap_mangen/tests/common.rs
@@ -45,7 +45,7 @@ pub fn special_commands_command(name: &'static str) -> clap::Command<'static> {
                 .about("tests other things")
                 .arg(
                     clap::Arg::new("config")
-                        .long("--config")
+                        .long("config")
                         .takes_value(true)
                         .help("the other case to test"),
                 ),
@@ -128,7 +128,7 @@ pub fn sub_subcommands_command(name: &'static str) -> clap::Command<'static> {
             .subcommand(
                 clap::Command::new("sub_cmd").about("sub-subcommand").arg(
                     clap::Arg::new("config")
-                        .long("--config")
+                        .long("config")
                         .takes_value(true)
                         .possible_values([clap::PossibleValue::new("Lest quotes aren't escaped.")])
                         .help("the other case to test"),
@@ -222,10 +222,10 @@ pub fn value_hint_command(name: &'static str) -> clap::Command<'static> {
 
 pub fn hidden_option_command(name: &'static str) -> clap::Command<'static> {
     clap::Command::new(name)
-        .arg(clap::Arg::new("config").long("--config").takes_value(true))
+        .arg(clap::Arg::new("config").long("config").takes_value(true))
         .arg(
             clap::Arg::new("no-config")
-                .long("--no-config")
+                .long("no-config")
                 .hide(true)
                 .overrides_with("config"),
         )
diff --git a/src/bin/stdio-fixture.rs b/src/bin/stdio-fixture.rs
index bb04cada8f2..e3f34b41a22 100644
--- a/src/bin/stdio-fixture.rs
+++ b/src/bin/stdio-fixture.rs
@@ -6,7 +6,7 @@ fn main() {
         .subcommand(clap::Command::new("more"))
         .arg(
             clap::Arg::new("verbose")
-                .long("--verbose")
+                .long("verbose")
                 .help("log")
                 .long_help("more log"),
         );
diff --git a/src/build/arg.rs b/src/build/arg.rs
index 6f73b4c02c2..80c5199dfb8 100644
--- a/src/build/arg.rs
+++ b/src/build/arg.rs
@@ -200,7 +200,14 @@ impl<'help> Arg<'help> {
     #[inline]
     #[must_use]
     pub fn long(mut self, l: &'help str) -> Self {
-        self.long = Some(l.trim_start_matches(|c| c == '-'));
+        #[cfg(feature = "unstable-v4")]
+        {
+            self.long = Some(l);
+        }
+        #[cfg(not(feature = "unstable-v4"))]
+        {
+            self.long = Some(l.trim_start_matches(|c| c == '-'));
+        }
         self
     }
 
@@ -1819,7 +1826,7 @@ impl<'help> Arg<'help> {
     /// # use clap::{Command, Arg};
     /// let m = Command::new("pv")
     ///     .arg(Arg::new("option")
-    ///         .long("--option")
+    ///         .long("option")
     ///         .takes_value(true)
     ///         .ignore_case(true)
     ///         .possible_value("test123"))
@@ -1837,7 +1844,7 @@ impl<'help> Arg<'help> {
     /// let m = Command::new("pv")
     ///     .arg(Arg::new("option")
     ///         .short('o')
-    ///         .long("--option")
+    ///         .long("option")
     ///         .takes_value(true)
     ///         .ignore_case(true)
     ///         .multiple_values(true)
diff --git a/src/build/command.rs b/src/build/command.rs
index 097872c1619..4ba7c844727 100644
--- a/src/build/command.rs
+++ b/src/build/command.rs
@@ -2263,7 +2263,14 @@ impl<'help> App<'help> {
     /// [`Arg::long`]: Arg::long()
     #[must_use]
     pub fn long_flag(mut self, long: &'help str) -> Self {
-        self.long_flag = Some(long.trim_start_matches(|c| c == '-'));
+        #[cfg(feature = "unstable-v4")]
+        {
+            self.long_flag = Some(long);
+        }
+        #[cfg(not(feature = "unstable-v4"))]
+        {
+            self.long_flag = Some(long.trim_start_matches(|c| c == '-'));
+        }
         self
     }
 
diff --git a/src/build/debug_asserts.rs b/src/build/debug_asserts.rs
index 1bbf86a6130..90f1b7e0d91 100644
--- a/src/build/debug_asserts.rs
+++ b/src/build/debug_asserts.rs
@@ -45,6 +45,10 @@ pub(crate) fn assert_app(cmd: &Command) {
         }
 
         if let Some(l) = sc.get_long_flag().as_ref() {
+            #[cfg(feature = "unstable-v4")]
+            {
+                assert!(!l.starts_with('-'), "Command {}: long_flag {:?} must not start with a `-`, that will be handled by the parser", sc.get_name(), l);
+            }
             long_flags.push(Flag::Command(format!("--{}", l), sc.get_name()));
         }
 
@@ -75,6 +79,10 @@ pub(crate) fn assert_app(cmd: &Command) {
         }
 
         if let Some(l) = arg.long.as_ref() {
+            #[cfg(feature = "unstable-v4")]
+            {
+                assert!(!l.starts_with('-'), "Argument {}: long {:?} must not start with a `-`, that will be handled by the parser", arg.name, l);
+            }
             long_flags.push(Flag::Arg(format!("--{}", l), &*arg.name));
         }
 
diff --git a/tests/builder/flags.rs b/tests/builder/flags.rs
index 343cc3a979b..fd8a4301b44 100644
--- a/tests/builder/flags.rs
+++ b/tests/builder/flags.rs
@@ -179,3 +179,20 @@ For more information try --help
 
     utils::assert_output(cmd, "test -----", MULTIPLE_DASHES, true);
 }
+
+#[test]
+#[cfg(not(feature = "unstable-v4"))]
+fn leading_dash_stripped() {
+    let cmd = Command::new("mycat").arg(Arg::new("filename").long("--filename"));
+    let matches = cmd.try_get_matches_from(["mycat", "--filename"]).unwrap();
+    assert!(matches.is_present("filename"));
+}
+
+#[test]
+#[cfg(feature = "unstable-v4")]
+#[cfg(debug_assertions)]
+#[should_panic = "Argument filename: long \"--filename\" must not start with a `-`, that will be handled by the parser"]
+fn leading_dash_stripped() {
+    let cmd = Command::new("mycat").arg(Arg::new("filename").long("--filename"));
+    cmd.debug_assert();
+}
diff --git a/tests/builder/possible_values.rs b/tests/builder/possible_values.rs
index 58e6bd55fc8..ccf17239732 100644
--- a/tests/builder/possible_values.rs
+++ b/tests/builder/possible_values.rs
@@ -134,7 +134,7 @@ fn possible_values_of_option() {
         .arg(
             Arg::new("option")
                 .short('o')
-                .long("--option")
+                .long("option")
                 .takes_value(true)
                 .possible_value("test123"),
         )
@@ -153,7 +153,7 @@ fn possible_values_of_option_fail() {
         .arg(
             Arg::new("option")
                 .short('o')
-                .long("--option")
+                .long("option")
                 .takes_value(true)
                 .possible_value("test123"),
         )
@@ -169,7 +169,7 @@ fn possible_values_of_option_multiple() {
         .arg(
             Arg::new("option")
                 .short('o')
-                .long("--option")
+                .long("option")
                 .takes_value(true)
                 .possible_value("test123")
                 .possible_value("test321")
@@ -193,7 +193,7 @@ fn possible_values_of_option_multiple_fail() {
         .arg(
             Arg::new("option")
                 .short('o')
-                .long("--option")
+                .long("option")
                 .takes_value(true)
                 .possible_value("test123")
                 .possible_value("test321")
@@ -298,7 +298,7 @@ fn alias() {
         .arg(
             Arg::new("option")
                 .short('o')
-                .long("--option")
+                .long("option")
                 .takes_value(true)
                 .possible_value(PossibleValue::new("test123").alias("123"))
                 .possible_value("test321")
@@ -316,7 +316,7 @@ fn aliases() {
         .arg(
             Arg::new("option")
                 .short('o')
-                .long("--option")
+                .long("option")
                 .takes_value(true)
                 .possible_value(PossibleValue::new("test123").aliases(["1", "2", "3"]))
                 .possible_value("test321")
@@ -334,7 +334,7 @@ fn ignore_case() {
         .arg(
             Arg::new("option")
                 .short('o')
-                .long("--option")
+                .long("option")
                 .takes_value(true)
                 .possible_value("test123")
                 .possible_value("test321")
@@ -356,7 +356,7 @@ fn ignore_case_fail() {
         .arg(
             Arg::new("option")
                 .short('o')
-                .long("--option")
+                .long("option")
                 .takes_value(true)
                 .possible_value("test123")
                 .possible_value("test321"),
@@ -373,7 +373,7 @@ fn ignore_case_multiple() {
         .arg(
             Arg::new("option")
                 .short('o')
-                .long("--option")
+                .long("option")
                 .takes_value(true)
                 .possible_value("test123")
                 .possible_value("test321")
@@ -395,7 +395,7 @@ fn ignore_case_multiple_fail() {
         .arg(
             Arg::new("option")
                 .short('o')
-                .long("--option")
+                .long("option")
                 .takes_value(true)
                 .possible_value("test123")
                 .possible_value("test321")
diff --git a/tests/builder/unicode.rs b/tests/builder/unicode.rs
index e3de1b1856b..dc97787b246 100644
--- a/tests/builder/unicode.rs
+++ b/tests/builder/unicode.rs
@@ -6,7 +6,7 @@ fn possible_values_ignore_case() {
         .arg(
             clap::Arg::new("option")
                 .short('o')
-                .long("--option")
+                .long("option")
                 .takes_value(true)
                 .possible_value("ä")
                 .ignore_case(true),