diff --git a/hledger-lib/Hledger/Data/Json.hs b/hledger-lib/Hledger/Data/Json.hs
index 90c0f43a1..6478d5dfb 100644
--- a/hledger-lib/Hledger/Data/Json.hs
+++ b/hledger-lib/Hledger/Data/Json.hs
@@ -41,8 +41,8 @@ import           Data.Aeson
 import           Data.Aeson.Encode.Pretty (encodePrettyToTextBuilder)
 --import           Data.Aeson.TH
 import qualified Data.ByteString.Lazy as BL
-import           Data.Decimal
-import           Data.Maybe
+import           Data.Decimal (DecimalRaw(..), roundTo)
+import           Data.Maybe (fromMaybe)
 import qualified Data.Text.Lazy    as TL
 import qualified Data.Text.Lazy.IO as TL
 import qualified Data.Text.Lazy.Builder as TB
@@ -80,13 +80,13 @@ instance ToJSON GenericSourcePos
 -- and that the overall number of significant digits in the floating point
 -- remains manageable in practice. (I'm not sure how to limit the number
 -- of significant digits in a Decimal right now.)
-instance ToJSON Decimal where
+instance (Integral a, ToJSON a) => ToJSON (DecimalRaw a) where
   toJSON d = object
-    ["decimalPlaces"   .= toJSON decimalPlaces
-    ,"decimalMantissa" .= toJSON decimalMantissa
-    ,"floatingPoint"   .= toJSON (fromRational $ toRational d' :: Double)
-    ]
-    where d'@Decimal{..} = roundTo 10 d
+      [ "decimalPlaces"   .= toJSON (decimalPlaces d')
+      , "decimalMantissa" .= toJSON (decimalMantissa d')
+      , "floatingPoint"   .= toJSON (realToFrac d' :: Double)
+      ]
+    where d' = if decimalPlaces d <= 10 then d else roundTo 10 d
 
 instance ToJSON Amount
 instance ToJSON AmountStyle
diff --git a/hledger/test/json.test b/hledger/test/json.test
index 229378e77..1a970981f 100644
--- a/hledger/test/json.test
+++ b/hledger/test/json.test
@@ -18,8 +18,8 @@ $ hledger -f- reg --output-format=json
                     "acommodity": "AAA",
                     "aquantity": {
                         "floatingPoint": 1,
-                        "decimalPlaces": 10,
-                        "decimalMantissa": 10000000000
+                        "decimalPlaces": 1,
+                        "decimalMantissa": 10
                     },
                     "aismultiplier": false,
                     "astyle": {
@@ -46,8 +46,8 @@ $ hledger -f- reg --output-format=json
                 "acommodity": "AAA",
                 "aquantity": {
                     "floatingPoint": 1,
-                    "decimalPlaces": 10,
-                    "decimalMantissa": 10000000000
+                    "decimalPlaces": 1,
+                    "decimalMantissa": 10
                 },
                 "aismultiplier": false,
                 "astyle": {
@@ -76,8 +76,8 @@ $ hledger -f- bal --output-format=json
                     "acommodity": "AAA",
                     "aquantity": {
                         "floatingPoint": 1,
-                        "decimalPlaces": 10,
-                        "decimalMantissa": 10000000000
+                        "decimalPlaces": 1,
+                        "decimalMantissa": 10
                     },
                     "aismultiplier": false,
                     "astyle": {
@@ -97,8 +97,8 @@ $ hledger -f- bal --output-format=json
             "acommodity": "AAA",
             "aquantity": {
                 "floatingPoint": 1,
-                "decimalPlaces": 10,
-                "decimalMantissa": 10000000000
+                "decimalPlaces": 1,
+                "decimalMantissa": 10
             },
             "aismultiplier": false,
             "astyle": {