diff --git a/crates/uv-pep508/src/marker/parse.rs b/crates/uv-pep508/src/marker/parse.rs
index 9c361c19d..de8bfac72 100644
--- a/crates/uv-pep508/src/marker/parse.rs
+++ b/crates/uv-pep508/src/marker/parse.rs
@@ -5,7 +5,7 @@ use uv_pep440::{Version, VersionPattern, VersionSpecifier};
 
 use crate::cursor::Cursor;
 use crate::marker::MarkerValueExtra;
-use crate::marker::tree::{ContainerOperator, MarkerValueDependencyGroup};
+use crate::marker::tree::{ContainerOperator, MarkerValueContains, MarkerValueDependencyGroup};
 use crate::{
     ExtraOperator, MarkerExpression, MarkerOperator, MarkerTree, MarkerValue, MarkerValueString,
     MarkerValueVersion, MarkerWarningKind, Pep508Error, Pep508ErrorSource, Pep508Url, Reporter,
@@ -209,10 +209,9 @@ pub(crate) fn parse_marker_key_op_value<T: Pep508Url>(
         MarkerValue::MarkerEnvString(key) => {
             let value = match r_value {
                 MarkerValue::Extra
-                | MarkerValue::Extras
-                | MarkerValue::DependencyGroups
                 | MarkerValue::MarkerEnvVersion(_)
-                | MarkerValue::MarkerEnvString(_) => {
+                | MarkerValue::MarkerEnvString(_)
+                | MarkerValue::MarkerEnvContains(_) => {
                     reporter.report(
                         MarkerWarningKind::MarkerMarkerComparison,
                         "Comparing two markers with each other doesn't make any sense,
@@ -245,9 +244,8 @@ pub(crate) fn parse_marker_key_op_value<T: Pep508Url>(
             let value = match r_value {
                 MarkerValue::MarkerEnvVersion(_)
                 | MarkerValue::MarkerEnvString(_)
-                | MarkerValue::Extra
-                | MarkerValue::Extras
-                | MarkerValue::DependencyGroups => {
+                | MarkerValue::MarkerEnvContains(_)
+                | MarkerValue::Extra => {
                     reporter.report(
                         MarkerWarningKind::ExtraInvalidComparison,
                         "Comparing extra with something other than a quoted string is wrong,
@@ -279,9 +277,11 @@ pub(crate) fn parse_marker_key_op_value<T: Pep508Url>(
                 // `'...' == extra`
                 MarkerValue::Extra => parse_extra_expr(operator, &l_string, reporter),
                 // `'...' in extras`
-                MarkerValue::Extras => parse_extras_expr(operator, &l_string, reporter),
+                MarkerValue::MarkerEnvContains(MarkerValueContains::Extras) => {
+                    parse_extras_expr(operator, &l_string, reporter)
+                }
                 // `'...' in dependency_groups`
-                MarkerValue::DependencyGroups => {
+                MarkerValue::MarkerEnvContains(MarkerValueContains::DependencyGroups) => {
                     parse_dependency_groups_expr(operator, &l_string, reporter)
                 }
                 // `'...' == '...'`, doesn't make much sense
@@ -300,22 +300,12 @@ pub(crate) fn parse_marker_key_op_value<T: Pep508Url>(
                 }
             }
         }
-        MarkerValue::Extras => {
+        MarkerValue::MarkerEnvContains(key) => {
             reporter.report(
                 MarkerWarningKind::Pep440Error,
                 format!(
-                    "The `extras` marker must be used as '...' in extras' or '... not in extras',
-                    found `{l_value} {operator} {r_value}`, will be ignored"
-                ),
-            );
-            return Ok(None);
-        }
-        MarkerValue::DependencyGroups => {
-            reporter.report(
-                MarkerWarningKind::Pep440Error,
-                format!(
-                    "The `dependency_groups` marker must be used as '...' in dependency_groups' or '... not in dependency_groups',
-                    found `{l_value} {operator} {r_value}`, will be ignored"
+                    "The `{key}` marker must be used as '...' in {key}' or '... not in {key}',
+                    found `{key} {operator} {r_value}`, will be ignored"
                 ),
             );
             return Ok(None);
diff --git a/crates/uv-pep508/src/marker/tree.rs b/crates/uv-pep508/src/marker/tree.rs
index 594b81723..95e7327ed 100644
--- a/crates/uv-pep508/src/marker/tree.rs
+++ b/crates/uv-pep508/src/marker/tree.rs
@@ -126,6 +126,24 @@ impl Display for MarkerValueString {
     }
 }
 
+/// Those markers with exclusively `in` and `not in` operators (PEP 751)
+#[derive(Clone, Debug, Eq, Hash, PartialEq, PartialOrd, Ord)]
+pub enum MarkerValueContains {
+    /// `extras`. This one is special because it's a list, and user-provided
+    Extras,
+    /// `dependency_groups`. This one is special because it's a list, and user-provided
+    DependencyGroups,
+}
+
+impl Display for MarkerValueContains {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::Extras => f.write_str("extras"),
+            Self::DependencyGroups => f.write_str("dependency_groups"),
+        }
+    }
+}
+
 /// One of the predefined environment values
 ///
 /// <https://packaging.python.org/en/latest/specifications/dependency-specifiers/#environment-markers>
@@ -137,10 +155,8 @@ pub enum MarkerValue {
     MarkerEnvString(MarkerValueString),
     /// `extra`. This one is special because it's a list, and user-provided
     Extra,
-    /// `extras`. This one is special because it's a list, and user-provided
-    Extras,
-    /// `dependency_groups`. This one is special because it's a list, and user-provided
-    DependencyGroups,
+    /// Those markers with exclusively `in` and `not in` operators (PEP 751)
+    MarkerEnvContains(MarkerValueContains),
     /// Not a constant, but a user given quoted string with a value inside such as '3.8' or "windows"
     QuotedString(ArcStr),
 }
@@ -181,8 +197,8 @@ impl FromStr for MarkerValue {
             "sys_platform" => Self::MarkerEnvString(MarkerValueString::SysPlatform),
             "sys.platform" => Self::MarkerEnvString(MarkerValueString::SysPlatformDeprecated),
             "extra" => Self::Extra,
-            "extras" => Self::Extras,
-            "dependency_groups" => Self::DependencyGroups,
+            "extras" => Self::MarkerEnvContains(MarkerValueContains::Extras),
+            "dependency_groups" => Self::MarkerEnvContains(MarkerValueContains::DependencyGroups),
             _ => return Err(format!("Invalid key: {s}")),
         };
         Ok(value)
@@ -195,8 +211,7 @@ impl Display for MarkerValue {
             Self::MarkerEnvVersion(marker_value_version) => marker_value_version.fmt(f),
             Self::MarkerEnvString(marker_value_string) => marker_value_string.fmt(f),
             Self::Extra => f.write_str("extra"),
-            Self::Extras => f.write_str("extras"),
-            Self::DependencyGroups => f.write_str("dependency_groups"),
+            Self::MarkerEnvContains(marker_value_contains) => marker_value_contains.fmt(f),
             Self::QuotedString(value) => write!(f, "'{value}'"),
         }
     }