diff --git a/src/Data/BigInt/Argonaut.js b/src/Data/BigInt/Argonaut.js
index 1a137e5..a99f3f2 100644
--- a/src/Data/BigInt/Argonaut.js
+++ b/src/Data/BigInt/Argonaut.js
@@ -17,7 +17,7 @@ exports.restoreJson = function (original) {
 }
 
 exports.decodeBigInt = function (fail, succ, json) {
-    if (typeof json === "number" || typeof json === "bigint") {
+    if (Number.isInteger(json) || typeof json === "bigint") {
         return succ(bigInt(json));
     } else {
         return fail;
@@ -25,5 +25,12 @@ exports.decodeBigInt = function (fail, succ, json) {
 }
 
 exports.encodeBigInt = function (a) {
-    return bigInt(a);
+    if (JSON.stringify !== JSONbig.stringify) {
+        console.warn(
+            "Tried to encode BitInt without patching JSON.stringify. Wrap your app in Data.BigInt.Argonaut.withJsonPatch."
+        );
+        return a.toJSNumber();
+    } else {
+        return a.value;
+    }
 }
diff --git a/test/Data/BigInt/Argonaut/Spec.purs b/test/Data/BigInt/Argonaut/Spec.purs
new file mode 100644
index 0000000..5aa6ece
--- /dev/null
+++ b/test/Data/BigInt/Argonaut/Spec.purs
@@ -0,0 +1,54 @@
+module Data.BigInt.Argonaut.Spec
+  ( bigIntSpec
+  ) where
+
+import Prologue
+
+import Data.Argonaut.Decode (JsonDecodeError)
+import Data.Argonaut.Extra (encodeStringifyJson, parseDecodeJson)
+import Data.BigInt as BI
+import Data.BigInt.Argonaut (BigInt, fromInt, withJsonPatch)
+import Data.Newtype (unwrap)
+import Data.String (codePointFromChar, dropWhile, null)
+import Data.String.Gen (genDigitString)
+import Test.QuickCheck (class Arbitrary, (===))
+import Test.QuickCheck.Gen (suchThat)
+import Test.Spec (Spec, around_, describe, it)
+import Test.Spec.Assertions (shouldNotEqual)
+import Test.Spec.QuickCheck (quickCheck)
+
+newtype DigitString = DigitString String
+
+instance arbitraryDigitString :: Arbitrary DigitString where
+  arbitrary =
+    map DigitString
+      $ flip suchThat (not null)
+      $ map (dropWhile (eq (codePointFromChar '0')))
+      $ genDigitString
+
+bigIntSpec :: Spec Unit
+bigIntSpec =
+  describe "Data.BigInt.Argonaut" do
+    around_ withJsonPatch $ it "obeys the roundtrip law under withJsonPatch" do
+      quickCheck \(DigitString s) ->
+        let
+          decoded :: Either JsonDecodeError BigInt
+          decoded = parseDecodeJson s
+        in
+          encodeStringifyJson <$> decoded === Right s
+    it "does not always obey the roundtrip law when not under withJsonPatch" do
+      let
+        s = "23457890122347890123478901234123409871234"
+
+        decoded :: Either JsonDecodeError BigInt
+        decoded = parseDecodeJson s
+      (encodeStringifyJson <$> decoded) `shouldNotEqual` Right s
+    around_ withJsonPatch $ it "decodes a valid BigInt" do
+      quickCheck \(DigitString s) ->
+        let
+          decoded :: Either JsonDecodeError BigInt
+          decoded = parseDecodeJson s
+        in
+          (unwrap <<< add (fromInt 10))
+            <$> decoded === (add (BI.fromInt 10) <<< unwrap)
+            <$> decoded
diff --git a/test/Main.purs b/test/Main.purs
index 4cf7cb5..b64cb90 100644
--- a/test/Main.purs
+++ b/test/Main.purs
@@ -3,7 +3,7 @@ module Test.Main where
 import Prologue
 
 import Data.Array.Extra.Spec (arrayExtraSpec)
-import Data.BigInt.Argonaut (withJsonPatch)
+import Data.BigInt.Argonaut.Spec (bigIntSpec)
 import Data.Cursor.Spec (cursorSpec)
 import Data.Foldable.Extra.Spec (foldableExtraSpec)
 import Data.String.Extra.Spec (stringExtraSpec)
@@ -16,10 +16,10 @@ import Test.Spec.Runner (runSpec)
 main :: Effect Unit
 main =
   launchAff_ do
-    withJsonPatch do
-      runSpec [ consoleReporter ] do
-        cursorSpec
-        arrayExtraSpec
-        foldableExtraSpec
-        stringExtraSpec
-        assocMapSpec
+    runSpec [ consoleReporter ] do
+      cursorSpec
+      arrayExtraSpec
+      foldableExtraSpec
+      stringExtraSpec
+      assocMapSpec
+      bigIntSpec