diff --git a/hledger-lib/Hledger/Data/Transaction.hs b/hledger-lib/Hledger/Data/Transaction.hs
index 4eac78d00..4c9cc0979 100644
--- a/hledger-lib/Hledger/Data/Transaction.hs
+++ b/hledger-lib/Hledger/Data/Transaction.hs
@@ -59,6 +59,7 @@ module Hledger.Data.Transaction (
 )
 where
 import Data.List
+import Data.List.Extra (nubSort)
 import Data.Maybe
 import Data.Text (Text)
 import qualified Data.Text as T
@@ -339,31 +340,55 @@ transactionPostingBalances t = (sumPostings $ realPostings t
                                ,sumPostings $ virtualPostings t
                                ,sumPostings $ balancedVirtualPostings t)
 
--- | Check that this transaction appears balanced when rendered,
--- returning an appropriate error message if it is not.
--- In more detail: after converting amounts to cost using explicit
--- transaction prices if any; and summing the real postings; and
--- summing the balanced virtual postings; and applying the given
--- display styles, if provided (maybe affecting decimal places):
--- do both posting totals appear to be zero when rendered ?
+-- | Check that this transaction would appear balanced to a human when displayed,
+-- and return an appropriate error message otherwise.
+--
+-- In more detail:
+-- For the real postings, and separately for the balanced virtual postings:
+--
+-- 1. Convert amounts to cost where possible
+--
+-- 2. When there are multiple amounts which appear non-zero when displayed
+--    (using the given display styles if provided),
+--    are they a mix of positives and negatives ?
+--    This is checked separately to give a clearer error message.
+--    (Best effort, could be confused by postings with multicommodity amounts.)
+--
+-- 3. Does the amounts' sum appear non-zero when displayed ?
+--    (using the given display styles if provided)
+--
 transactionCheckBalanced :: Maybe (M.Map CommoditySymbol AmountStyle) -> Transaction -> Maybe String
 transactionCheckBalanced mstyles t 
-  | rbalanced && bvbalanced = Nothing
-  | otherwise = Just $ printf "could not balance this transaction (%s%s%s)" rmsg sep bvmsg
+  | rsignsok && bvsignsok && rzerosum && bvzerosum = Nothing
+  | otherwise = Just msg
   where
-    (rsum, _, bvsum)            = transactionPostingBalances t
+    (rps, bvps) = (realPostings t, balancedVirtualPostings t)
+    canonicalise = maybe id canonicaliseMixedAmount mstyles
+
+    -- check mixed signs, detecting nonzeros at display precision
+    nonZeros ps = filter (not.isZeroMixedAmount) $ map (canonicalise.costOfMixedAmount.pamount) ps
+    signsOk ps = 
+      case nonZeros ps of
+        nzs | length nzs > 1 -> length (nubSort $ mapMaybe isNegativeMixedAmount nzs) > 1
+        _ -> True
+    (rsignsok, bvsignsok)       = (signsOk rps, signsOk bvps)
+
+    -- check zero sum, at display precision
+    (rsum, bvsum)               = (sumPostings rps, sumPostings bvps)
     (rsumcost, bvsumcost)       = (costOfMixedAmount rsum, costOfMixedAmount bvsum)
     (rsumdisplay, bvsumdisplay) = (canonicalise rsumcost, canonicalise bvsumcost)
-      where canonicalise = maybe id canonicaliseMixedAmount mstyles
-    -- for checking balanced, use the display precision
-    (rbalanced, bvbalanced)     = (isZeroMixedAmount rsumdisplay, isZeroMixedAmount bvsumdisplay)
-    -- for selecting and generating error messages, use the uncanonicalised full precision
-    -- XXX always correct ?
-    rmsg | isReallyZeroMixedAmount rsumcost = ""
-         | otherwise = "real postings are off by " ++ showMixedAmount rsumcost
-    bvmsg | isReallyZeroMixedAmount bvsumcost = ""
-          | otherwise = "balanced virtual postings are off by " ++ showMixedAmount bvsumcost
-    sep = if not (null rmsg) && not (null bvmsg) then "; " else "" :: String
+    (rzerosum, bvzerosum)       = (isZeroMixedAmount rsumdisplay, isZeroMixedAmount bvsumdisplay)
+
+    -- select & generate error messages, showing amounts with their original precision
+    rmsg
+      | not rsignsok  = "real postings all have the same sign"
+      | not rzerosum  = "real postings' sum should be 0 but is: " ++ showMixedAmount rsumcost
+      | otherwise     = "" 
+    bvmsg
+      | not bvsignsok = "balanced virtual postings all have the same sign"
+      | not bvzerosum = "balanced virtual postings' sum should be 0 but is: " ++ showMixedAmount bvsumcost
+      | otherwise     = "" 
+    msg = intercalate "\n" $ ["could not balance this transaction:"] ++ filter (not.null) [rmsg, bvmsg]
 
 -- | Legacy form of transactionCheckBalanced.
 isTransactionBalanced :: Maybe (M.Map CommoditySymbol AmountStyle) -> Transaction -> Bool
@@ -403,7 +428,7 @@ balanceTransactionHelper mstyles t = do
     Just err -> Left $ annotateErrorWithTransaction t' err
 
 annotateErrorWithTransaction :: Transaction -> String -> String
-annotateErrorWithTransaction t s = intercalate "\n" [showGenericSourcePos $ tsourcepos t, s, showTransaction t]
+annotateErrorWithTransaction t s = unlines [showGenericSourcePos $ tsourcepos t, s, showTransaction t]
 
 -- | Infer up to one missing amount for this transactions's real postings, and
 -- likewise for its balanced virtual postings, if needed; or return an error
diff --git a/tests/journal/parse-errors.test b/tests/journal/parse-errors.test
index 87295df28..fa4aa6310 100644
--- a/tests/journal/parse-errors.test
+++ b/tests/journal/parse-errors.test
@@ -19,23 +19,18 @@ expecting date separator or digit
 
 # A journal with an unbalanced transaction.
 <
-2018/1/1
-  a  1
+2009/1/1
+  a   1
 
-# 2. When read from stdin with no reader prefix, the journal reader is used,
-# and fails here. (Before 1.17, all readers were tried and the timedot reader
-# would succeed.)
+# 2. When read from stdin with no reader prefix, the journal reader is used
+# (before 1.17, all readers were tried and the timedot reader would succeed),
+# giving an unbalanced error in this case.
 $ hledger -f - print
->2 /could not balance/
+>2 /real postings' sum should be 0 but is: 1/
 >=1
 
-# 3. So in these tests we must sometimes force the desired format, like so.
-# Now we see the error from the journal reader.
-$ hledger -f journal:- print
->2 /could not balance this transaction \(real postings are off by 1\)/
->=1
-
-# 4. We expect to have reference to line number with last posting
+# 3. We expect to have reference to line number with last posting
+# NB: \< and \> match start and end of a word.
 $ hledger -f journal:- print
 >2 /\<2\>/
 >=1
@@ -45,7 +40,7 @@ $ hledger -f journal:- print
 2018/1/1
   (a) 1
 
-# 5. hledger doesn't detect this as an error directly, it parses account name "(a) 1" and
+# 4. hledger doesn't detect this as an error directly, it parses account name "(a) 1" and
 # amount 0 here.
 $ hledger -f - print -x
 2018-01-01
@@ -53,7 +48,7 @@ $ hledger -f - print -x
 
 >=
 
-# 6. Two (or more) postings with implicit amount cannot be balanced.
+# 5. Two (or more) postings with implicit amount cannot be balanced.
 <
 2018/1/1
   a  1
@@ -64,7 +59,7 @@ $ hledger -f journal:- print
 >2 /could not balance this transaction - can't have more than one real posting with no amount/
 >=1
 
-# 7. Two (or more) virtual postings with implicit amount cannot be balanced.
+# 6. Two (or more) virtual postings with implicit amount cannot be balanced.
 # (And the error message contains line numbers).
 <
 2018/1/1
@@ -75,3 +70,64 @@ $ hledger -f journal:- print
 $ hledger -f journal:- print
 >2 /lines 1-4/
 >=1
+
+# 7. Balancing error messages show the recorded precision, not the display precision.
+<
+2010/1/1
+   a  1C @ $1.0049
+   a  $-1.000
+$ hledger -f- print
+>2 /real postings' sum should be 0 but is: \$0.0049/
+>=1
+
+# 8. Multiple postings all with the same sign gets a distinct error message.
+<
+2020-01-01
+  a  1A
+  b  1A
+$ hledger -f- print
+>2 /real postings all have the same sign/
+>=1
+
+# 9. Zeros don't trigger the same sign error.
+<
+2020-01-01
+  a  A 0
+  b  B 0
+$ hledger -f- print
+2020-01-01
+    a               0
+    b               0
+
+>=0
+
+# 10. An inferred multicommodity amount doesn't trigger the same sign error.
+<
+2020-01-01
+    a  A 1
+    b  B 1
+    c
+$ hledger -f- print
+2020-01-01
+    a             A 1
+    b             B 1
+    c
+
+>=0
+
+# 11. For multiple postings all with the same sign but in different commodities,
+# the error should show the original amounts, without inferring transaction prices.
+<
+2020-01-01
+  a  1A
+  b  1B
+$ hledger -f- print
+>2
+hledger: "-" (lines 1-3)
+could not balance this transaction:
+real postings all have the same sign
+2020-01-01
+    a        1A @@ 1B
+    b              1B
+
+>=1
diff --git a/tests/journal/precision.test b/tests/journal/precision.test
index 2a5907b98..d6a83d8d3 100644
--- a/tests/journal/precision.test
+++ b/tests/journal/precision.test
@@ -38,7 +38,7 @@ hledger -f - balance --no-total --cost --empty
 2010/1/1
    a  1C @ $1.0049
    a  $-1.000
->>>2 /off by \$0.0049/
+>>>2 /should be 0 but is: \$0.0049/
 >>>= 1
 
 # 4. with $'s display precision at 2 or less, this txn should balance
diff --git a/tests/journal/unbalanced.test b/tests/journal/unbalanced.test
deleted file mode 100644
index 393e839a9..000000000
--- a/tests/journal/unbalanced.test
+++ /dev/null
@@ -1,7 +0,0 @@
-hledger -f - register
-<<<
-2009/1/1 a
-  b  1.1
-  c  -1
->>>2 /could not balance this transaction \(real postings are off by 0.1\)/
->>>= 1