diff --git a/generic/models.py b/generic/models.py
index c14ea5be..99ec9da4 100644
--- a/generic/models.py
+++ b/generic/models.py
@@ -783,10 +783,12 @@ class ExamOrCollectionGenericBase(models.Model, AuthorMixin):
             if self.start_date >= timezone.now() or (
                 self.end_date is not None and self.end_date <= timezone.now()
             ):
-                raise Http404("Exam not found")
+                # Raise with an explanatory message so the frontend can
+                # surface the reason to the end user.
+                raise Http404("Exam not currently available (outside allowed dates)")
         # If it is not active no one can take
         elif active_only and not self.active:
-            raise Http404("Exam not found")
+            raise Http404("Exam currently inactive")
 
         # If candidates only check they have access
         if self.candidates_only: