diff --git a/resources/test/fixtures/flake8_no_pep420/test_pass_pyi/example.pyi b/resources/test/fixtures/flake8_no_pep420/test_pass_pyi/example.pyi
new file mode 100644
index 00000000000000..e69de29bb2d1d6
diff --git a/src/rules/flake8_no_pep420/mod.rs b/src/rules/flake8_no_pep420/mod.rs
index 04d38aeff3e5b2..e19a2112228550 100644
--- a/src/rules/flake8_no_pep420/mod.rs
+++ b/src/rules/flake8_no_pep420/mod.rs
@@ -13,21 +13,20 @@ mod tests {
     use crate::registry::Rule;
     use crate::settings::Settings;
 
-    #[test_case(Path::new("test_pass_init"); "INP001_0")]
-    #[test_case(Path::new("test_fail_empty"); "INP001_1")]
-    #[test_case(Path::new("test_fail_nonempty"); "INP001_2")]
-    #[test_case(Path::new("test_fail_shebang"); "INP001_3")]
-    #[test_case(Path::new("test_ignored"); "INP001_4")]
-    #[test_case(Path::new("test_pass_namespace_package"); "INP001_5")]
-    fn test_flake8_no_pep420(path: &Path) -> Result<()> {
+    #[test_case(Path::new("test_pass_init"), Path::new("example.py"); "INP001_0")]
+    #[test_case(Path::new("test_fail_empty"), Path::new("example.py"); "INP001_1")]
+    #[test_case(Path::new("test_fail_nonempty"), Path::new("example.py"); "INP001_2")]
+    #[test_case(Path::new("test_fail_shebang"), Path::new("example.py"); "INP001_3")]
+    #[test_case(Path::new("test_ignored"), Path::new("example.py"); "INP001_4")]
+    #[test_case(Path::new("test_pass_namespace_package"), Path::new("example.py"); "INP001_5")]
+    #[test_case(Path::new("test_pass_pyi"), Path::new("example.pyi"); "INP001_6")]
+    fn test_flake8_no_pep420(path: &Path, filename: &Path) -> Result<()> {
         let snapshot = format!("{}", path.to_string_lossy());
-        // Platform-independent paths
-        let p = PathBuf::from(format!(
-            "./resources/test/fixtures/flake8_no_pep420/{}/example.py",
-            path.display()
-        ));
         let diagnostics = test_path(
-            p.as_path(),
+            Path::new("./resources/test/fixtures/flake8_no_pep420")
+                .join(path)
+                .join(filename)
+                .as_path(),
             &Settings {
                 namespace_packages: vec![PathBuf::from(
                     "./resources/test/fixtures/flake8_no_pep420/test_pass_namespace_package",
diff --git a/src/rules/flake8_no_pep420/rules.rs b/src/rules/flake8_no_pep420/rules.rs
index 07d1fe9ba53f8d..abd95def73112d 100644
--- a/src/rules/flake8_no_pep420/rules.rs
+++ b/src/rules/flake8_no_pep420/rules.rs
@@ -20,7 +20,7 @@ impl Violation for ImplicitNamespacePackage {
 
 /// INP001
 pub fn implicit_namespace_package(path: &Path, package: Option<&Path>) -> Option<Diagnostic> {
-    if package.is_none() {
+    if package.is_none() && path.extension().map_or(false, |ext| ext == "py") {
         Some(Diagnostic::new(
             ImplicitNamespacePackage(fs::relativize_path(path)),
             Range::default(),
diff --git a/src/rules/flake8_no_pep420/snapshots/ruff__rules__flake8_no_pep420__tests__test_pass_pyi.snap b/src/rules/flake8_no_pep420/snapshots/ruff__rules__flake8_no_pep420__tests__test_pass_pyi.snap
new file mode 100644
index 00000000000000..622ebcff04079e
--- /dev/null
+++ b/src/rules/flake8_no_pep420/snapshots/ruff__rules__flake8_no_pep420__tests__test_pass_pyi.snap
@@ -0,0 +1,6 @@
+---
+source: src/rules/flake8_no_pep420/mod.rs
+expression: diagnostics
+---
+[]
+