diff --git a/crates/uv-pep440/src/version_specifier.rs b/crates/uv-pep440/src/version_specifier.rs
index aff917179e1f0..155585fb2cee2 100644
--- a/crates/uv-pep440/src/version_specifier.rs
+++ b/crates/uv-pep440/src/version_specifier.rs
@@ -573,7 +573,10 @@ impl VersionSpecifier {
                         .version
                         .release()
                         .iter()
-                        .zip(&*other.release())
+                        // Pad the version with zeros if it's shorter than the specifier
+                        // prefix, e.g., version "2" (== "2.0") should NOT match "==2.1.*"
+                        // because 2.0 != 2.1.
+                        .zip(other.release().iter().chain(std::iter::repeat(&0)))
                         .all(|(this, other)| this == other)
             }
             #[allow(deprecated)]
@@ -590,7 +593,10 @@ impl VersionSpecifier {
                     || !this
                         .release()
                         .iter()
-                        .zip(&*version.release())
+                        // Pad the version with zeros if it's shorter than the specifier
+                        // prefix, e.g., version "2" (== "2.0") should match "!=2.1.*"
+                        // because 2.0 != 2.1.
+                        .zip(other.release().iter().chain(std::iter::repeat(&0)))
                         .all(|(this, other)| this == other)
             }
             Operator::TildeEqual => {
@@ -1272,6 +1278,58 @@ mod tests {
         );
     }
 
+    #[test]
+    fn test_equal_star_short_version_bug() {
+        // Version "2" (equivalent to 2.0) should NOT match "==2.1.*"
+        let specifier = VersionSpecifier::from_str("==2.1.*").unwrap();
+        let version = Version::from_str("2").unwrap();
+        assert!(
+            !specifier.contains(&version),
+            "Bug: version '2' incorrectly matches '==2.1.*'"
+        );
+
+        // Version "2" (equivalent to 2.0) SHOULD match "!=2.1.*"
+        let specifier = VersionSpecifier::from_str("!=2.1.*").unwrap();
+        let version = Version::from_str("2").unwrap();
+        assert!(
+            specifier.contains(&version),
+            "Bug: version '2' should match '!=2.1.*' (2.0 is not in 2.1 family)"
+        );
+
+        // Verify existing behavior still works: "2" matches "==2.0.*"
+        let specifier = VersionSpecifier::from_str("==2.0.*").unwrap();
+        let version = Version::from_str("2").unwrap();
+        assert!(
+            specifier.contains(&version),
+            "version '2' should match '==2.0.*'"
+        );
+
+        // And "2" should NOT match "!=2.0.*"
+        let specifier = VersionSpecifier::from_str("!=2.0.*").unwrap();
+        let version = Version::from_str("2").unwrap();
+        assert!(
+            !specifier.contains(&version),
+            "version '2' should not match '!=2.0.*'"
+        );
+
+        // Local versions: local segment should be ignored for prefix matching.
+        // "2+local" (== "2.0") should NOT match "==2.1.*"
+        let specifier = VersionSpecifier::from_str("==2.1.*").unwrap();
+        let version = Version::from_str("2+local").unwrap();
+        assert!(
+            !specifier.contains(&version),
+            "version '2+local' should not match '==2.1.*'"
+        );
+
+        // "2+local" (== "2.0") SHOULD match "!=2.1.*"
+        let specifier = VersionSpecifier::from_str("!=2.1.*").unwrap();
+        let version = Version::from_str("2+local").unwrap();
+        assert!(
+            specifier.contains(&version),
+            "version '2+local' should match '!=2.1.*'"
+        );
+    }
+
     #[test]
     fn test_specifiers_true() {
         let pairs = [