diff --git a/crates/turborepo-repository/src/discovery.rs b/crates/turborepo-repository/src/discovery.rs
index f6f9c616c4aee..e09a35b3be306 100644
--- a/crates/turborepo-repository/src/discovery.rs
+++ b/crates/turborepo-repository/src/discovery.rs
@@ -104,6 +104,11 @@ impl LocalPackageDiscoveryBuilder {
     pub fn with_allow_no_package_manager(&mut self, allow_missing_package_manager: bool) {
         self.allow_missing_package_manager = allow_missing_package_manager;
     }
+
+    pub fn with_package_manager(&mut self, package_manager: Option<PackageManager>) -> &mut Self {
+        self.package_manager = package_manager;
+        self
+    }
 }
 
 impl PackageDiscoveryBuilder for LocalPackageDiscoveryBuilder {
diff --git a/crates/turborepo-repository/src/package_graph/builder.rs b/crates/turborepo-repository/src/package_graph/builder.rs
index 406d1f1e7180b..d4956fb9b6c64 100644
--- a/crates/turborepo-repository/src/package_graph/builder.rs
+++ b/crates/turborepo-repository/src/package_graph/builder.rs
@@ -80,6 +80,12 @@ impl<'a> PackageGraphBuilder<'a, LocalPackageDiscoveryBuilder> {
             .with_allow_no_package_manager(allow_no_package_manager);
         self
     }
+
+    pub fn with_package_manager(mut self, package_manager: PackageManager) -> Self {
+        self.package_discovery
+            .with_package_manager(Some(package_manager));
+        self
+    }
 }
 
 impl<'a, P> PackageGraphBuilder<'a, P> {
diff --git a/packages/turbo-repository/__tests__/affected-packages.test.ts b/packages/turbo-repository/__tests__/affected-packages.test.ts
index 7c4a1008fea10..9ac9cd084a3df 100644
--- a/packages/turbo-repository/__tests__/affected-packages.test.ts
+++ b/packages/turbo-repository/__tests__/affected-packages.test.ts
@@ -59,6 +59,22 @@ describe("affectedPackages", () => {
     });
   }
 
+  it("does not require packageManager for npm", async () => {
+    const dir = path.resolve(__dirname, "./fixtures/npm-monorepo");
+    const workspace = await Workspace.find(dir);
+
+    const reduced: PackageReduced[] = (
+      await workspace.affectedPackages(["apps/app/file.txt"])
+    ).map((pkg) => {
+      return {
+        name: pkg.name,
+        relativePath: pkg.relativePath,
+      };
+    });
+
+    assert.deepEqual(reduced, [{ name: "app-a", relativePath: "apps/app" }]);
+  });
+
   describe("optimizedLockfileUpdates", () => {
     it("errors if not provided comparison ref", async () => {
       const dir = path.resolve(__dirname, "./fixtures/monorepo");
diff --git a/packages/turbo-repository/__tests__/fixtures/npm-monorepo/apps/app/package.json b/packages/turbo-repository/__tests__/fixtures/npm-monorepo/apps/app/package.json
new file mode 100644
index 0000000000000..18fa556034020
--- /dev/null
+++ b/packages/turbo-repository/__tests__/fixtures/npm-monorepo/apps/app/package.json
@@ -0,0 +1,6 @@
+{
+  "name": "app-a",
+  "dependencies": {
+    "ui": "*"
+  }
+}
diff --git a/packages/turbo-repository/__tests__/fixtures/npm-monorepo/package-lock.json b/packages/turbo-repository/__tests__/fixtures/npm-monorepo/package-lock.json
new file mode 100644
index 0000000000000..dbc1ef31910ee
--- /dev/null
+++ b/packages/turbo-repository/__tests__/fixtures/npm-monorepo/package-lock.json
@@ -0,0 +1,34 @@
+{
+  "name": "basic",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "basic",
+      "workspaces": [
+        "apps/*",
+        "packages/*"
+      ]
+    },
+    "apps/app": {
+      "name": "app-a",
+      "dependencies": {
+        "ui": "*"
+      }
+    },
+    "node_modules/app-a": {
+      "resolved": "apps/app",
+      "link": true
+    },
+    "node_modules/blank": {
+      "resolved": "packages/blank",
+      "link": true
+    },
+    "node_modules/ui": {
+      "resolved": "packages/ui",
+      "link": true
+    },
+    "packages/blank": {},
+    "packages/ui": {}
+  }
+}
diff --git a/packages/turbo-repository/__tests__/fixtures/npm-monorepo/package.json b/packages/turbo-repository/__tests__/fixtures/npm-monorepo/package.json
new file mode 100644
index 0000000000000..7236271b8f467
--- /dev/null
+++ b/packages/turbo-repository/__tests__/fixtures/npm-monorepo/package.json
@@ -0,0 +1,5 @@
+{
+  "name": "basic",
+  "private": true,
+  "workspaces": ["apps/*", "packages/*"]
+}
diff --git a/packages/turbo-repository/__tests__/fixtures/npm-monorepo/packages/blank/package.json b/packages/turbo-repository/__tests__/fixtures/npm-monorepo/packages/blank/package.json
new file mode 100644
index 0000000000000..b0de282a25e06
--- /dev/null
+++ b/packages/turbo-repository/__tests__/fixtures/npm-monorepo/packages/blank/package.json
@@ -0,0 +1,3 @@
+{
+  "//": "missing name field in this package.json"
+}
diff --git a/packages/turbo-repository/__tests__/fixtures/npm-monorepo/packages/ui/package.json b/packages/turbo-repository/__tests__/fixtures/npm-monorepo/packages/ui/package.json
new file mode 100644
index 0000000000000..1cd75b539ecc2
--- /dev/null
+++ b/packages/turbo-repository/__tests__/fixtures/npm-monorepo/packages/ui/package.json
@@ -0,0 +1,3 @@
+{
+  "name": "ui"
+}
diff --git a/packages/turbo-repository/rust/src/internal.rs b/packages/turbo-repository/rust/src/internal.rs
index 770fea1b05817..511f92c4332c0 100644
--- a/packages/turbo-repository/rust/src/internal.rs
+++ b/packages/turbo-repository/rust/src/internal.rs
@@ -63,19 +63,22 @@ impl Workspace {
             })?;
         let workspace_state = WorkspaceState::infer(&reference_dir)?;
         let is_multi_package = workspace_state.mode == WorkspaceType::MultiPackage;
-        let package_manager_name = workspace_state
-            .package_manager
-            .as_ref()
-            .map_err(|error| Error::PackageManager {
-                error: error.to_string(),
-                path: workspace_state.root.clone(),
-            })?
-            .name();
+        let package_manager =
+            workspace_state
+                .package_manager
+                .as_ref()
+                .map_err(|error| Error::PackageManager {
+                    error: error.to_string(),
+                    path: workspace_state.root.clone(),
+                })?;
+
+        let package_manager_name = package_manager.name();
 
         let workspace_root = &workspace_state.root;
         let root_package_json = PackageJson::load(&workspace_root.join_component("package.json"))?;
         let package_graph = PackageGraphBuilder::new(workspace_root, root_package_json)
             .with_single_package_mode(!is_multi_package)
+            .with_package_manager(package_manager.clone())
             .build()
             .await?;