diff --git a/Ledger/Entry.hs b/Ledger/Entry.hs
index 75ce754b0..05cce0c96 100644
--- a/Ledger/Entry.hs
+++ b/Ledger/Entry.hs
@@ -26,8 +26,13 @@ isEntryBalanced (Entry {etransactions=ts}) = isZeroAmount sum && numcommodities=
       sum = sumLedgerTransactions ts
       numcommodities = length $ nub $ map (symbol . commodity . tamount) ts
 
+-- | Fill in a missing balance in this entry, if there is one, 
+-- or raise an error if there is more than one.
 autofillEntry :: Entry -> Entry
-autofillEntry e@(Entry {etransactions=ts}) = e{etransactions=autofillTransactions ts}
+autofillEntry e@(Entry {etransactions=ts}) = e{etransactions=ts'}
+    where ts' = fromMaybe 
+                (error $ "too many blank transactions in this entry:\n" ++ show e)
+                (autofillTransactions ts)
 
 assertBalancedEntry :: Entry -> Entry
 assertBalancedEntry e
diff --git a/Ledger/RawTransaction.hs b/Ledger/RawTransaction.hs
index f55d859f0..a2d042a5a 100644
--- a/Ledger/RawTransaction.hs
+++ b/Ledger/RawTransaction.hs
@@ -21,12 +21,14 @@ showRawTransaction t = (showaccountname $ taccount t) ++ " " ++ (showamount $ ta
       showaccountname = printf "%-22s" . elideAccountName 22
       showamount = printf "%12s" . showAmountOrZero
 
-autofillTransactions :: [RawTransaction] -> [RawTransaction]
+-- | Fill in the missing balance in an entry's transactions. There can be
+-- at most one missing balance, otherwise we'll return Nothing.
+autofillTransactions :: [RawTransaction] -> Maybe [RawTransaction]
 autofillTransactions ts =
     case (length blanks) of
-      0 -> ts
-      1 -> map balance ts
-      otherwise -> error "too many blank transactions in this entry"
+      0 -> Just ts
+      1 -> Just $ map balance ts
+      otherwise -> Nothing
     where 
       (normals, blanks) = partition isnormal ts
       isnormal t = (symbol $ commodity $ tamount t) /= "AUTO"