diff --git a/src/Handler/Utils/Exam.hs b/src/Handler/Utils/Exam.hs
index 3ed6e30db..211f27e4a 100644
--- a/src/Handler/Utils/Exam.hs
+++ b/src/Handler/Utils/Exam.hs
@@ -267,8 +267,8 @@ examAutoOccurrence :: forall seed.
                    -> Map UserId (User, Maybe ExamOccurrenceId)
                    -> (Maybe (ExamOccurrenceMapping ExamOccurrenceId), Map UserId (Maybe ExamOccurrenceId))
 examAutoOccurrence (hash -> seed) rule ExamAutoOccurrenceConfig{..} occurrences users
-  | sum occurrences < usersCount
-    || sum occurrences <= 0
+  | sum occurrences' < usersCount
+    || sum occurrences' <= 0
     || Map.null users
   = nullResult
   | otherwise
@@ -277,7 +277,7 @@ examAutoOccurrence (hash -> seed) rule ExamAutoOccurrenceConfig{..} occurrences
         -> ( Nothing
            , flip Map.mapWithKey users $ \uid (_, mOcc)
                -> let randomOcc = flip evalRand (mkStdGen $ hashWithSalt seed uid) $
-                        weighted $ over _2 fromIntegral <$> occurrences'
+                        weighted $ over _2 fromIntegral <$> occurrences''
                    in Just $ fromMaybe randomOcc mOcc
            )
       _ | Just (postprocess -> (resMapping, result)) <- bestOption
@@ -309,21 +309,28 @@ examAutoOccurrence (hash -> seed) rule ExamAutoOccurrenceConfig{..} occurrences
             in Map.mapKeysWith Set.union (take . F.minimum . Set.map length $ Map.keysSet matrUsers) matrUsers
       _ -> Map.singleton [] $ Map.keysSet users
 
+    occurrences' :: Map ExamOccurrenceId Natural
+    -- ^ reduce room capacity for every pre-assigned user by 1
+    occurrences' = foldl' (flip $ Map.adjust predOrZero) occurrences $ Map.mapMaybe snd users
+      where
+        predOrZero :: Natural -> Natural
+        predOrZero 0 = 0
+        predOrZero n = pred n
 
-    occurrences' :: [(ExamOccurrenceId, Natural)]
+    occurrences'' :: [(ExamOccurrenceId, Natural)]
     -- ^ Minimise number of occurrences used
     --
     -- Prefer occurrences with higher capacity
     --
     -- If a single occurrence can accommodate all participants, pick the one with
     -- the least capacity
-    occurrences'
+    occurrences''
       | not eaocMinimizeRooms
-      = Map.toList occurrences
-      | Just largeEnoughs <- fromNullable . filter ((>= usersCount) . view _2) $ Map.toList occurrences
+      = Map.toList occurrences'
+      | Just largeEnoughs <- fromNullable . filter ((>= usersCount) . view _2) $ Map.toList occurrences'
       = pure $ minimumBy (comparing $ view _2) largeEnoughs
       | otherwise
-      = view _2 . foldl' accF (0, []) . sortOn (Down . view _2) $ Map.toList occurrences
+      = view _2 . foldl' accF (0, []) . sortOn (Down . view _2) $ Map.toList occurrences'
       where
         accF :: (Natural, [(ExamOccurrenceId, Natural)])
              -> (ExamOccurrenceId, Natural)
@@ -469,7 +476,7 @@ examAutoOccurrence (hash -> seed) rule ExamAutoOccurrenceConfig{..} occurrences
     charCost :: [CI Char] -> [CI Char] -> Extended Rational
     charCost pA pB = Finite (max 1 $ List.genericLength (pA `lcp` pB) * eaocFinenessCost * fromIntegral longestLine) ^ 2
       where
-        longestLine = maximum . mapNonNull (view _2) $ impureNonNull occurrences'
+        longestLine = maximum . mapNonNull (view _2) $ impureNonNull occurrences''
 
 
     lcp :: Eq a => [a] -> [a] -> [a]
@@ -485,7 +492,7 @@ examAutoOccurrence (hash -> seed) rule ExamAutoOccurrenceConfig{..} occurrences
     bestOption :: Maybe [(ExamOccurrenceId, [[CI Char]])]
     bestOption = case rule of
       ExamRoomSurname -> do
-        (_cost, res) <- distribute (sortBy (RFC5051.compareUnicode `on` (pack . toListOf (_1 . folded . to CI.foldedCase))) . Map.toAscList $ fromIntegral . Set.size <$> users') occurrences' lineNudges charCost
+        (_cost, res) <- distribute (sortBy (RFC5051.compareUnicode `on` (pack . toListOf (_1 . folded . to CI.foldedCase))) . Map.toAscList $ fromIntegral . Set.size <$> users') occurrences'' lineNudges charCost
         -- traceM $ show cost
         return res
       ExamRoomMatriculation -> do
@@ -493,7 +500,7 @@ examAutoOccurrence (hash -> seed) rule ExamAutoOccurrenceConfig{..} occurrences
             -- finenessCost n = Finite (max 1 $ fromIntegral n * eaocFinenessCost * fromIntegral longestLine) ^ 2 * length occurrences'
 
             distributeFine :: Natural -> Maybe (Extended Rational, _)
-            distributeFine n = distribute (usersFineness n) occurrences' lineNudges charCost
+            distributeFine n = distribute (usersFineness n) occurrences'' lineNudges charCost
 
             maximumFineness = fromIntegral . F.minimum . Set.map length $ Map.keysSet users'