diff --git a/src/Data.Buffer.Immutable.BigInt.js b/src/Data.Buffer.Immutable.BigInt.js
index 930f3db..1a865f8 100644
--- a/src/Data.Buffer.Immutable.BigInt.js
+++ b/src/Data.Buffer.Immutable.BigInt.js
@@ -1,11 +1,11 @@
 import { Buffer } from 'node:buffer'
 
 /** @type {(offset: number) => (b: Buffer) => bigint} */
-export const readBigUInt64BE = off => b => b.readBigUInt64BE(off)
+export const readBigInt64BE = off => b => b.readBigInt64BE(off)
 
 /** @type {(b: bigint) => Buffer} */
-export const fromBigUInt64BE = b => {
+export const fromBigInt64BE = b => {
   const buf = Buffer.alloc(8)
-  buf.writeBigUInt64BE(b)
+  buf.writeBigInt64BE(b)
   return buf
 }
diff --git a/src/Data.Buffer.Immutable.BigInt.purs b/src/Data.Buffer.Immutable.BigInt.purs
index e3d381f..8bc3748 100644
--- a/src/Data.Buffer.Immutable.BigInt.purs
+++ b/src/Data.Buffer.Immutable.BigInt.purs
@@ -3,5 +3,5 @@ module Data.Buffer.Immutable.BigInt where
 import JS.BigInt (BigInt)
 import Node.Buffer.Immutable (ImmutableBuffer)
 
-foreign import readBigUInt64BE :: Int -> ImmutableBuffer -> BigInt
-foreign import fromBigUInt64BE :: BigInt -> ImmutableBuffer
+foreign import readBigInt64BE :: Int -> ImmutableBuffer -> BigInt
+foreign import fromBigInt64BE :: BigInt -> ImmutableBuffer
diff --git a/src/Data.Proquint.purs b/src/Data.Proquint.purs
index 40f3caa..ca11a5c 100644
--- a/src/Data.Proquint.purs
+++ b/src/Data.Proquint.purs
@@ -256,21 +256,21 @@ fromString s = map (trim <<< Proquint) $ traverse segmentFromString $ String.spl
 fromInt :: Int -> Proquint
 fromInt n = fromBits $ unsafePerformEffect do
   buf <- Buffer.alloc 4
-  Buffer.write Buffer.UInt32BE (Int.toNumber n) 0 buf
+  Buffer.write Buffer.Int32BE (Int.toNumber n) 0 buf
   Buffer.freeze buf
 
 toInt :: Proquint -> Maybe Int
 toInt pq@(Proquint segs)
-  | Array.length segs <= 2 = Int.fromNumber $ Buffer.Immutable.read UInt32BE 0 $ toBits $ pad 2 pq
+  | Array.length segs <= 2 = Int.fromNumber $ Buffer.Immutable.read Int32BE 0 $ toBits $ pad 2 pq
   | otherwise = Nothing
 
 toBigInt :: Proquint -> Maybe BigInt
 toBigInt pq@(Proquint segs)
-  | Array.length segs <= 4 = Just $ Buffer.Immutable.BigInt.readBigUInt64BE 0 $ toBits $ pad 4 pq
+  | Array.length segs <= 4 = Just $ Buffer.Immutable.BigInt.readBigInt64BE 0 $ toBits $ pad 4 pq
   | otherwise = Nothing
 
 fromBigInt :: BigInt -> Proquint
-fromBigInt b = fromBits $ Buffer.Immutable.BigInt.fromBigUInt64BE b
+fromBigInt b = fromBits $ Buffer.Immutable.BigInt.fromBigInt64BE b
 
 toBits :: Proquint -> ImmutableBuffer
 toBits (Proquint segments) = unsafePerformEffect do
diff --git a/test/Test.Main.purs b/test/Test.Main.purs
index 2edac01..551ee54 100644
--- a/test/Test.Main.purs
+++ b/test/Test.Main.purs
@@ -46,7 +46,12 @@ genBigInt =
     bit true = "1"
     bit false = "0"
   in
-    map (bigintFromString <<< boolArrayToBinary) $ sequence $ Array.replicate 64 (arbitrary @Boolean)
+    do
+      sign <- map (if _ then identity else negate) $ arbitrary @Boolean
+      map (sign <<< bigintFromString <<< boolArrayToBinary)
+        $ sequence
+        $ Array.replicate 63
+        $ arbitrary @Boolean
 
 newtype TestCon = TestCon Con