diff --git a/package-lock.json b/package-lock.json
index 2ea0e1d..d464eaa 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -36,7 +36,7 @@
         "eslint-plugin-functional": "^4.0.2",
         "eslint-plugin-import": "^2.25.3",
         "eslint-plugin-prettier": "^4.0.0",
-        "fast-check": "^2.14.0",
+        "fast-check": "^2.25.0",
         "gh-pages": "^3.2.3",
         "husky": "^7.0.4",
         "ignore-loader": "^0.1.2",
@@ -5052,8 +5052,9 @@
     },
     "node_modules/fast-check": {
       "version": "2.25.0",
+      "resolved": "https://registry.npmjs.org/fast-check/-/fast-check-2.25.0.tgz",
+      "integrity": "sha512-wRUT2KD2lAmT75WNIJIHECawoUUMHM0I5jrlLXGtGeqmPL8jl/EldUDjY1VCp6fDY8yflyfUeIOsOBrIbIiArg==",
       "dev": true,
-      "license": "MIT",
       "dependencies": {
         "pure-rand": "^5.0.1"
       },
@@ -14684,6 +14685,8 @@
     },
     "fast-check": {
       "version": "2.25.0",
+      "resolved": "https://registry.npmjs.org/fast-check/-/fast-check-2.25.0.tgz",
+      "integrity": "sha512-wRUT2KD2lAmT75WNIJIHECawoUUMHM0I5jrlLXGtGeqmPL8jl/EldUDjY1VCp6fDY8yflyfUeIOsOBrIbIiArg==",
       "dev": true,
       "requires": {
         "pure-rand": "^5.0.1"
diff --git a/package.json b/package.json
index 5f2cd3c..e2b93ba 100644
--- a/package.json
+++ b/package.json
@@ -76,7 +76,7 @@
     "eslint-plugin-functional": "^4.0.2",
     "eslint-plugin-import": "^2.25.3",
     "eslint-plugin-prettier": "^4.0.0",
-    "fast-check": "^2.14.0",
+    "fast-check": "^2.25.0",
     "gh-pages": "^3.2.3",
     "husky": "^7.0.4",
     "ignore-loader": "^0.1.2",
diff --git a/src/epoch.spec.ts b/src/epoch.spec.ts
new file mode 100644
index 0000000..ac06245
--- /dev/null
+++ b/src/epoch.spec.ts
@@ -0,0 +1,17 @@
+import { expect } from "chai";
+import fc from "fast-check";
+
+import { epochBytesToInt, epochIntToBytes } from "./epoch.js";
+
+describe("epoch serialization", () => {
+  it("Round trip", async function () {
+    await fc.assert(
+      fc.asyncProperty(fc.integer({ min: 0 }), async (date) => {
+        const bytes = epochIntToBytes(date);
+        const _date = epochBytesToInt(bytes);
+
+        expect(_date.valueOf()).to.eq(date.valueOf());
+      })
+    );
+  });
+});
diff --git a/src/epoch.ts b/src/epoch.ts
index 3a14bd2..b87c975 100644
--- a/src/epoch.ts
+++ b/src/epoch.ts
@@ -5,7 +5,16 @@ const DefaultEpochUnitSeconds = 10; // the rln-relay epoch length in seconds
 export function dateToEpoch(
   timestamp: Date,
   epochUnitSeconds: number = DefaultEpochUnitSeconds
-): Uint8Array {
-  const unix = Math.floor(timestamp.getTime() / 1000 / epochUnitSeconds);
-  return writeUIntLE(new Uint8Array(32), unix, 0, 8);
+): number {
+  const time = timestamp.getTime();
+  return Math.floor(time / 1000 / epochUnitSeconds);
+}
+
+export function epochIntToBytes(epoch: number): Uint8Array {
+  return writeUIntLE(new Uint8Array(32), epoch, 0, 8);
+}
+
+export function epochBytesToInt(bytes: Uint8Array): number {
+  const dv = new DataView(bytes.buffer);
+  return dv.getUint32(0, true);
 }
diff --git a/src/rln.ts b/src/rln.ts
index d82931d..62b04b5 100644
--- a/src/rln.ts
+++ b/src/rln.ts
@@ -2,7 +2,7 @@ import init, * as zerokitRLN from "@waku/zerokit-rln-wasm";
 import { RateLimitProof } from "js-waku/lib/interfaces";
 
 import { writeUIntLE } from "./byte_utils.js";
-import { dateToEpoch } from "./epoch.js";
+import { dateToEpoch, epochIntToBytes } from "./epoch.js";
 import verificationKey from "./resources/verification_key.js";
 import * as wc from "./witness_calculator.js";
 import { WitnessCalculator } from "./witness_calculator.js";
@@ -152,9 +152,9 @@ export class RLNInstance {
     idKey: Uint8Array
   ): Promise<RateLimitProof> {
     if (epoch == undefined) {
-      epoch = dateToEpoch(new Date());
+      epoch = epochIntToBytes(dateToEpoch(new Date()));
     } else if (epoch instanceof Date) {
-      epoch = dateToEpoch(epoch);
+      epoch = epochIntToBytes(dateToEpoch(epoch));
     }
 
     if (epoch.length != 32) throw "invalid epoch";