diff --git a/crates/uv-resolver/src/preferences.rs b/crates/uv-resolver/src/preferences.rs
index 5683e8a17..c5fc760ee 100644
--- a/crates/uv-resolver/src/preferences.rs
+++ b/crates/uv-resolver/src/preferences.rs
@@ -163,7 +163,11 @@ impl PreferenceIndex {
         match self {
             Self::Any => true,
             Self::Implicit => false,
-            Self::Explicit(preference) => preference == index,
+            Self::Explicit(preference) => {
+                // Preferences are stored in the lockfile without credentials, while the index URL
+                // in locations such as `pyproject.toml` may contain credentials.
+                *preference.url() == *index.without_credentials()
+            }
         }
     }
 }
@@ -381,3 +385,30 @@ impl From<Version> for Pin {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::str::FromStr;
+
+    /// Test that [`PreferenceIndex::matches`] correctly ignores credentials when comparing URLs.
+    ///
+    /// This is relevant for matching lockfile preferences (stored without credentials)
+    /// against index URLs from pyproject.toml (which may include usernames for auth).
+    #[test]
+    fn test_preference_index_matches_ignores_credentials() {
+        // URL without credentials (as stored in lockfile)
+        let index_without_creds = IndexUrl::from_str("https:/pypi_index.com/simple").unwrap();
+
+        // URL with username (as specified in pyproject.toml)
+        let index_with_username =
+            IndexUrl::from_str("https://username@pypi_index.com/simple").unwrap();
+
+        let preference = PreferenceIndex::Explicit(index_without_creds.clone());
+
+        assert!(
+            preference.matches(&index_with_username),
+            "PreferenceIndex should match URLs that differ only in username"
+        );
+    }
+}
diff --git a/crates/uv/tests/it/lock.rs b/crates/uv/tests/it/lock.rs
index 6f7256932..6c9bd7858 100644
--- a/crates/uv/tests/it/lock.rs
+++ b/crates/uv/tests/it/lock.rs
@@ -9600,6 +9600,84 @@ fn lock_redact_https() -> Result<()> {
     Ok(())
 }
 
+/// Test that packages aren't unnecessarily updated when an index URL contains a username.
+#[test]
+fn lock_index_url_username_change_no_update() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    // Create initial lockfile with exact version constraint
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["anyio==4.0.0"]
+
+        [[tool.uv.index]]
+        name = "test-index"
+        url = "https://fakeuser@pypi.org/simple"
+
+        [tool.uv.sources]
+        anyio = { index = "test-index" }
+        "#,
+    )?;
+
+    uv_snapshot!(context.filters(), context.lock(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    "###);
+
+    let lock = context.read("uv.lock");
+
+    // Verify anyio 4.0.0 is locked
+    assert!(lock.contains("name = \"anyio\""));
+    assert!(lock.contains("version = \"4.0.0\""));
+
+    // Update pyproject.toml to simulate availability of newer package with more open but still compatible constraint
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["anyio>=4.0.0"]
+
+        [[tool.uv.index]]
+        name = "test-index"
+        url = "https://fakeuser@pypi.org/simple"
+
+        [tool.uv.sources]
+        anyio = { index = "test-index" }
+        "#,
+    )?;
+
+    // Run `uv lock`  to update the lockfile
+    // The package should stay at 4.0.0
+    uv_snapshot!(context.filters(), context.lock(), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    "###);
+
+    let lock_after = context.read("uv.lock");
+
+    assert!(
+        lock_after.contains("version = \"4.0.0\""),
+        "anyio should remain at version 4.0.0, not update despite >=4.0.0 constraint"
+    );
+
+    Ok(())
+}
+
 #[test]
 #[cfg(feature = "git")]
 fn lock_redact_git_pep508() -> Result<()> {