diff --git a/tasks/models.py b/tasks/models.py
index 66e0b0a..a88425c 100644
--- a/tasks/models.py
+++ b/tasks/models.py
@@ -156,9 +156,13 @@ class Task(models.Model):
             import pytz
 
             # Get current date in user's timezone
-            user_tz = pytz.timezone(self.user.timezone)
-            user_now = timezone.now().astimezone(user_tz)
-            user_today = user_now.date()
+            try:
+                user_tz = pytz.timezone(self.user.timezone)
+                user_now = timezone.now().astimezone(user_tz)
+                user_today = user_now.date()
+            except (pytz.UnknownTimeZoneError, AttributeError):
+                # Fall back to UTC if user timezone is invalid or missing
+                user_today = timezone.now().date()
 
             return self.due_date < user_today
         return False
diff --git a/tasks/views.py b/tasks/views.py
index a8ba166..c7ed0cb 100644
--- a/tasks/views.py
+++ b/tasks/views.py
@@ -220,9 +220,13 @@ class DashboardView(View):
 
         # Get today's date in user's timezone
         import pytz
-        user_tz = pytz.timezone(request.user.timezone)
-        user_now = timezone.now().astimezone(user_tz)
-        today = user_now.date()
+        try:
+            user_tz = pytz.timezone(request.user.timezone)
+            user_now = timezone.now().astimezone(user_tz)
+            today = user_now.date()
+        except (pytz.UnknownTimeZoneError, AttributeError):
+            # Fall back to UTC if user timezone is invalid or missing
+            today = timezone.now().date()
 
         # Get filter parameters
         current_filter = request.GET.get('filter', 'all')