diff --git a/CHANGELOG.md b/CHANGELOG.md
index c0f382aac..2644ad3f8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,3 +9,4 @@ All notable Modrinth Plus changes are documented here.
 - Added Windows installer publishing to the Gitea generic package registry.
 - Added Codex repository context and release/security documentation.
 - Fixed startup compatibility with existing official Modrinth App databases that recorded different checksums for historical SQLite migrations.
+- Fixed Connected Library Git repository URL resolution for repositories that use `master` instead of `main`.
diff --git a/packages/app-lib/src/api/connected_library.rs b/packages/app-lib/src/api/connected_library.rs
index fa30eaef1..11656c02a 100644
--- a/packages/app-lib/src/api/connected_library.rs
+++ b/packages/app-lib/src/api/connected_library.rs
@@ -157,9 +157,7 @@ pub async fn list() -> crate::Result<Vec<ConnectedPack>> {
 
 pub async fn connect(source_url: String) -> crate::Result<ConnectedPack> {
     let state = State::get().await?;
-    let manifest_url = normalize_manifest_url(&source_url)?;
-    let manifest = fetch_manifest(&manifest_url).await?;
-    validate_manifest(&manifest)?;
+    let (manifest_url, manifest) = resolve_manifest(&source_url).await?;
     upsert_manifest(&state.pool, None, &source_url, &manifest_url, &manifest)
         .await?;
     get_by_source(&state.pool, &source_url).await
@@ -197,14 +195,17 @@ pub async fn set_auto_update(
 pub async fn check(id: String) -> crate::Result<ConnectedCheckResult> {
     let state = State::get().await?;
     let pack = get_by_id(&state.pool, &id).await?;
-    let manifest = fetch_manifest(&pack.manifest_url).await?;
-    validate_manifest(&manifest)?;
+    let (manifest_url, manifest) = match fetch_manifest(&pack.manifest_url).await
+    {
+        Ok(manifest) => (pack.manifest_url.clone(), manifest),
+        Err(_) => resolve_manifest(&pack.source_url).await?,
+    };
 
     upsert_manifest(
         &state.pool,
         Some(&pack.id),
         &pack.source_url,
-        &pack.manifest_url,
+        &manifest_url,
         &manifest,
     )
     .await?;
@@ -306,7 +307,7 @@ pub async fn install(id: String) -> crate::Result<ConnectedPack> {
     get_by_id(&state.pool, &id).await
 }
 
-fn normalize_manifest_url(source_url: &str) -> crate::Result<String> {
+fn manifest_url_candidates(source_url: &str) -> crate::Result<Vec<String>> {
     let source = source_url.trim();
     let parsed = Url::parse(source)?;
 
@@ -318,7 +319,7 @@ fn normalize_manifest_url(source_url: &str) -> crate::Result<String> {
     }
 
     if source.ends_with(MANIFEST_FILE_NAME) || source.contains("/raw/") {
-        return Ok(source.to_string());
+        return Ok(vec![source.to_string()]);
     }
 
     let host = parsed.host_str().unwrap_or_default();
@@ -329,30 +330,52 @@ fn normalize_manifest_url(source_url: &str) -> crate::Result<String> {
 
     if host == "github.com" && segments.len() >= 2 {
         let repo = segments[1].trim_end_matches(".git");
-        return Ok(format!(
-            "https://raw.githubusercontent.com/{}/{}/main/{}",
-            segments[0], repo, MANIFEST_FILE_NAME
-        ));
+        return Ok(vec![
+            format!(
+                "https://raw.githubusercontent.com/{}/{}/main/{}",
+                segments[0], repo, MANIFEST_FILE_NAME
+            ),
+            format!(
+                "https://raw.githubusercontent.com/{}/{}/master/{}",
+                segments[0], repo, MANIFEST_FILE_NAME
+            ),
+        ]);
     }
 
     if host == "gitlab.com" && segments.len() >= 2 {
         let repo = segments[1].trim_end_matches(".git");
-        return Ok(format!(
-            "https://gitlab.com/{}/{}/-/raw/main/{}",
-            segments[0], repo, MANIFEST_FILE_NAME
-        ));
+        return Ok(vec![
+            format!(
+                "https://gitlab.com/{}/{}/-/raw/main/{}",
+                segments[0], repo, MANIFEST_FILE_NAME
+            ),
+            format!(
+                "https://gitlab.com/{}/{}/-/raw/master/{}",
+                segments[0], repo, MANIFEST_FILE_NAME
+            ),
+        ]);
     }
 
     if segments.len() >= 2 {
         let repo = segments[1].trim_end_matches(".git");
-        return Ok(format!(
-            "{}://{}/{}/{}/raw/branch/main/{}",
-            parsed.scheme(),
-            host,
-            segments[0],
-            repo,
-            MANIFEST_FILE_NAME
-        ));
+        return Ok(vec![
+            format!(
+                "{}://{}/{}/{}/raw/branch/main/{}",
+                parsed.scheme(),
+                host,
+                segments[0],
+                repo,
+                MANIFEST_FILE_NAME
+            ),
+            format!(
+                "{}://{}/{}/{}/raw/branch/master/{}",
+                parsed.scheme(),
+                host,
+                segments[0],
+                repo,
+                MANIFEST_FILE_NAME
+            ),
+        ]);
     }
 
     Err(ErrorKind::InputError(
@@ -362,6 +385,26 @@ fn normalize_manifest_url(source_url: &str) -> crate::Result<String> {
     .into())
 }
 
+async fn resolve_manifest(
+    source_url: &str,
+) -> crate::Result<(String, ConnectedManifest)> {
+    let candidates = manifest_url_candidates(source_url)?;
+    let mut errors = Vec::new();
+
+    for manifest_url in candidates {
+        match fetch_manifest(&manifest_url).await {
+            Ok(manifest) => return Ok((manifest_url, manifest)),
+            Err(err) => errors.push(format!("{manifest_url}: {err}")),
+        }
+    }
+
+    Err(ErrorKind::InputError(format!(
+        "Could not fetch {MANIFEST_FILE_NAME}. Tried: {}",
+        errors.join("; ")
+    ))
+    .into())
+}
+
 async fn fetch_manifest(url: &str) -> crate::Result<ConnectedManifest> {
     let manifest = reqwest::get(url)
         .await?