diff --git a/calibre-plugin/action.py b/calibre-plugin/action.py
index c4adf7f..d6f1941 100644
--- a/calibre-plugin/action.py
+++ b/calibre-plugin/action.py
@@ -265,7 +265,7 @@ def __get_loans_thread(self):
         thread.worker = worker
         thread.started.connect(worker.run)
 
-        def loaded(value):
+        def loaded(value: Dict):
             self.model.refresh_loans(value)
             self.refresh_btn.setEnabled(True)
             self.status_bar.clearMessage()
@@ -275,7 +275,7 @@ def loaded(value):
 
         return thread
 
-    def set_hide_books_already_in_library(self, checked):
+    def set_hide_books_already_in_library(self, checked: bool):
         PREFS[PreferenceKeys.HIDE_BOOKS_ALREADY_IN_LIB] = checked
         self.model.set_filter_hide_books_already_in_library(checked)
         self.loans_view.sortByColumn(-1, Qt.AscendingOrder)
@@ -291,7 +291,7 @@ def download_selected_loans(self):
                 self, _("Download"), _("Please select at least 1 loan."), show=True
             )
 
-    def download_loan(self, loan):
+    def download_loan(self, loan: Dict):
         format_id = LibbyClient.get_loan_format(
             loan, prefer_open_format=PREFS[PreferenceKeys.PREFER_OPEN_FORMATS]
         )
diff --git a/calibre-plugin/ebook_download.py b/calibre-plugin/ebook_download.py
index 151514a..b0025fa 100644
--- a/calibre-plugin/ebook_download.py
+++ b/calibre-plugin/ebook_download.py
@@ -65,7 +65,7 @@ def _custom_download(
         log=None,
         abort=None,
         notifications=None,
-    ):
+    ) -> str:
         temp_path = os.path.join(PersistentTemporaryDirectory(), filename)
         notifications.put((0.5, "Downloading"))
         res_content = libby_client.fulfill_loan_file(
diff --git a/calibre-plugin/magazine_download.py b/calibre-plugin/magazine_download.py
index 59c5c9e..555c598 100644
--- a/calibre-plugin/magazine_download.py
+++ b/calibre-plugin/magazine_download.py
@@ -391,7 +391,7 @@ def _custom_download(
         log=None,
         abort=None,
         notifications=None,
-    ):
+    ) -> str:
         logger = log
         download_progress_fraction = 0.97
         meta_progress_fraction = 1.0 - download_progress_fraction
diff --git a/calibre-plugin/model.py b/calibre-plugin/model.py
index 86480ff..2077fe0 100644
--- a/calibre-plugin/model.py
+++ b/calibre-plugin/model.py
@@ -1,4 +1,4 @@
-from typing import Dict
+from typing import Dict, Optional
 
 from calibre.ebooks.metadata.book.base import Metadata
 
@@ -46,7 +46,7 @@ def __init__(self, parent, synced_state=None, db=None):
         ]
         self.refresh_loans(synced_state)
 
-    def refresh_loans(self, synced_state=None):
+    def refresh_loans(self, synced_state: Optional[Dict] = None):
         if not synced_state:
             synced_state = {}
         self._cards = synced_state.get("cards", [])
diff --git a/calibre-plugin/worker.py b/calibre-plugin/worker.py
index 80941d1..1295f71 100644
--- a/calibre-plugin/worker.py
+++ b/calibre-plugin/worker.py
@@ -15,7 +15,7 @@ def __int__(self):
         super().__init__()
 
     def run(self):
-        libby_token = PREFS[PreferenceKeys.LIBBY_TOKEN]
+        libby_token: str = PREFS[PreferenceKeys.LIBBY_TOKEN]
         if not libby_token:
             self.finished.emit([])