diff --git a/internal/file/file.go b/internal/file/file.go
index 464db1cc..9dfcd12e 100644
--- a/internal/file/file.go
+++ b/internal/file/file.go
@@ -86,12 +86,12 @@ func CopyDirToDir(src, dst string) error {
 	if !fi.Mode().IsDir() {
 		return ErrNotDirectory
 	}
-	return filepath.WalkDir(src, func(path string, d fs.DirEntry, err error) error {
+	return filepath.WalkDir(src, func(filePath string, d fs.DirEntry, err error) error {
 		if err != nil {
 			return err
 		}
 		// skip sub-directories
-		if d.IsDir() && d.Name() != filepath.Base(path) {
+		if d.IsDir() && filePath != src {
 			return fs.SkipDir
 		}
 		info, err := d.Info()
@@ -100,7 +100,7 @@ func CopyDirToDir(src, dst string) error {
 		}
 		// only copy regular files
 		if info.Mode().IsRegular() {
-			return CopyToDir(path, dst)
+			return CopyToDir(filePath, dst)
 		}
 		return nil
 	})
diff --git a/internal/file/file_test.go b/internal/file/file_test.go
index aeeea399..f85b2468 100644
--- a/internal/file/file_test.go
+++ b/internal/file/file_test.go
@@ -171,6 +171,49 @@ func TestCopyToDir(t *testing.T) {
 	})
 }
 
+func TestCopyDirToDir(t *testing.T) {
+	t.Run("only top-level regular files are copied", func(t *testing.T) {
+		srcDir := t.TempDir()
+		destDir := t.TempDir()
+
+		// top-level regular file
+		if err := os.WriteFile(filepath.Join(srcDir, "top.txt"), []byte("top"), 0600); err != nil {
+			t.Fatal(err)
+		}
+		// a file nested in a sub-directory that must NOT be copied
+		subDir := filepath.Join(srcDir, "sub")
+		if err := os.MkdirAll(subDir, 0700); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(filepath.Join(subDir, "nested.txt"), []byte("nested"), 0600); err != nil {
+			t.Fatal(err)
+		}
+
+		if err := CopyDirToDir(srcDir, destDir); err != nil {
+			t.Fatal(err)
+		}
+
+		if _, err := os.Stat(filepath.Join(destDir, "top.txt")); err != nil {
+			t.Fatalf("expected top-level file to be copied, but got %v", err)
+		}
+		if _, err := os.Stat(filepath.Join(destDir, "nested.txt")); !os.IsNotExist(err) {
+			t.Fatal("expected sub-directory file to be skipped, but it was copied")
+		}
+	})
+
+	t.Run("source is not a directory", func(t *testing.T) {
+		srcDir := t.TempDir()
+		destDir := t.TempDir()
+		filename := filepath.Join(srcDir, "file.txt")
+		if err := os.WriteFile(filename, []byte("data"), 0600); err != nil {
+			t.Fatal(err)
+		}
+		if err := CopyDirToDir(filename, destDir); err != ErrNotDirectory {
+			t.Fatalf("expected ErrNotDirectory, but got %v", err)
+		}
+	})
+}
+
 func TestFileNameWithoutExtension(t *testing.T) {
 	input := "testfile.tar.gz"
 	expectedOutput := "testfile.tar"