diff --git a/beetsplug/unimported.py b/beetsplug/unimported.py
index 278fd667c..b473a346a 100644
--- a/beetsplug/unimported.py
+++ b/beetsplug/unimported.py
@@ -41,15 +41,17 @@ class Unimported(BeetsPlugin):
                 os.path.join(lib.directory, x.encode())
                 for x in self.config["ignore_subdirectories"].as_str_seq()
             ]
-            in_folder = {
-                os.path.join(r, file)
-                for r, d, f in os.walk(lib.directory)
-                for file in f
-                if not any(
-                    [file.endswith(ext) for ext in ignore_exts]
-                    + [r in ignore_dirs]
-                )
-            }
+            in_folder = set()
+            for root, _, files in os.walk(lib.directory):
+                # do not traverse if root is a child of an ignored directory
+                if any(root.startswith(ignored) for ignored in ignore_dirs):
+                    continue
+                for file in files:
+                    # ignore files with ignored extensions
+                    if any(file.endswith(ext) for ext in ignore_exts):
+                        continue
+                    in_folder.add(os.path.join(root, file))
+
             in_library = {x.path for x in lib.items()}
             art_files = {x.artpath for x in lib.albums()}
             for f in in_folder - in_library - art_files: