diff --git a/src/Juvix/Compiler/Concrete/Translation/FromSource.hs b/src/Juvix/Compiler/Concrete/Translation/FromSource.hs
index aff1337051..b75a497588 100644
--- a/src/Juvix/Compiler/Concrete/Translation/FromSource.hs
+++ b/src/Juvix/Compiler/Concrete/Translation/FromSource.hs
@@ -699,7 +699,7 @@ parsedFixityFields = do
     bel <- toPermutationWithDefault Nothing (Just <$> belowAbove kwBelow)
     abov <- toPermutationWithDefault Nothing (Just <$> belowAbove kwAbove)
     sam <- toPermutationWithDefault Nothing (Just <$> same)
-    -- This is a hack to allow an optional semicolon at the end
+    -- This is needed to allow an optional semicolon at the end
     toPermutationWithDefault Nothing (return (Just ()))
     pure (as, bel, abov, sam)
   r <- kw delimBraceR
@@ -771,7 +771,7 @@ parsedIteratorInfo = do
   (_parsedIteratorInfoInitNum, _parsedIteratorInfoRangeNum) <- intercalateEffect semicolon $ do
     ini <- toPermutationWithDefault Nothing (Just <$> pinit)
     ran <- toPermutationWithDefault Nothing (Just <$> prangeNum)
-    -- This is a hack to allow an optional semicolon at the end
+    -- This is needed to allow an optional semicolon at the end
     toPermutationWithDefault Nothing (return (Just ()))
     pure (ini, ran)
   r <- kw delimBraceR
diff --git a/src/Juvix/Data/Effect/ExactPrint/Base.hs b/src/Juvix/Data/Effect/ExactPrint/Base.hs
index 4ff677019d..1fd17ce248 100644
--- a/src/Juvix/Data/Effect/ExactPrint/Base.hs
+++ b/src/Juvix/Data/Effect/ExactPrint/Base.hs
@@ -28,6 +28,7 @@ data ExactPrint :: Effect where
   PrintCommentsUntil :: Interval -> ExactPrint m (Maybe SpaceSpan)
   EnsureEmptyLine :: ExactPrint m ()
   Region :: (Doc Ann -> Doc Ann) -> m b -> ExactPrint m b
+  -- | Both doc arguments are required to span the same region.
   RegionAlt :: (Doc Ann -> Doc Ann -> Doc Ann) -> (b -> b -> b) -> m b -> m b -> ExactPrint m b
   End :: ExactPrint m ()
 
@@ -91,6 +92,7 @@ runExactPrint cs = reinterpretH (runPrivateStateAsDoc (initialBuilder cs)) handl
               _builderEnsureEmptyLine = st' ^. builderEnsureEmptyLine
             }
         return fx
+      -- `m1` and `m2` are required to span the same region.
       RegionAlt regionModif alt (m1 :: Sem localEs x) (m2 :: Sem localEs x) -> do
         st0 :: Builder <- set builderDoc mempty <$> get
         let runner :: Sem (State Builder ': localEs) x -> Sem localEs (Builder, x)
@@ -106,6 +108,7 @@ runExactPrint cs = reinterpretH (runPrivateStateAsDoc (initialBuilder cs)) handl
             inner2 = localSeqUnliftCommon locEnv (helper m2)
         (st1 :: Builder, fx1) <- raise inner1
         (st2 :: Builder, fx2) <- raise inner2
+        massert (length (st1 ^. builderComments) == length (st2 ^. builderComments))
         doc' <- gets (^. builderDoc)
         put
           Builder