diff --git a/package.json b/package.json
index 5ae4cfe..606d0c4 100644
--- a/package.json
+++ b/package.json
@@ -34,11 +34,11 @@
     "circom_runtime": "0.0.3",
     "ffiasm": "0.0.2",
     "ffjavascript": "0.0.3",
-    "ffwasm": "0.0.5",
+    "ffwasm": "0.0.6",
     "fnv-plus": "^1.3.1",
-    "r1csfile": "0.0.2",
+    "r1csfile": "0.0.3",
     "tmp-promise": "^2.0.2",
-    "wasmbuilder": "0.0.9"
+    "wasmbuilder": "0.0.10"
   },
   "devDependencies": {
     "eslint": "^6.8.0",
diff --git a/src/r1csfile.js b/src/r1csfile.js
index f141f9a..51763a4 100644
--- a/src/r1csfile.js
+++ b/src/r1csfile.js
@@ -103,7 +103,11 @@ async function buildR1cs(ctx, fileName) {
 
     async function writeU64(v, pos) {
         const b = Buffer.allocUnsafe(8);
-        b.writeBigUInt64LE(BigInt(v));
+
+        const LSB = v & 0xFFFFFFFF;
+        const MSB = Math.floor(v / 0x100000000);
+        b.writeInt32LE(LSB, 0);
+        b.writeInt32LE(MSB, 4);
 
         await fd.write(b, 0, 8, pos);