diff --git a/contracts/Proofs.sol b/contracts/Proofs.sol
index aa9c3b2..a169506 100644
--- a/contracts/Proofs.sol
+++ b/contracts/Proofs.sol
@@ -71,7 +71,7 @@ abstract contract Proofs is Periods {
     pointer = _getPointer(id, period);
     bytes32 challenge = _getChallenge(pointer);
     uint256 probability = (_probabilities[id] * (256 - _config.downtime)) / 256;
-    isRequired = uint256(challenge) % probability == 0;
+    isRequired = probability == 0 || uint256(challenge) % probability == 0;
   }
 
   function _isProofRequired(
diff --git a/test/Proofs.test.js b/test/Proofs.test.js
index c1525f9..561ee9b 100644
--- a/test/Proofs.test.js
+++ b/test/Proofs.test.js
@@ -41,6 +41,7 @@ describe("Proofs", function () {
 
     it("requires proofs with an agreed upon probability", async function () {
       await proofs.startRequiringProofs(slotId, probability)
+      await advanceTime(period)
       let amount = 0
       for (let i = 0; i < 100; i++) {
         if (await proofs.isProofRequired(slotId)) {
@@ -52,6 +53,15 @@ describe("Proofs", function () {
       expect(amount).to.be.closeTo(expected, expected / 2)
     })
 
+    it("supports probability 1 (proofs are always required)", async function () {
+      await proofs.startRequiringProofs(slotId, 1)
+      await advanceTime(period)
+      while ((await proofs.getPointer(slotId)) < downtime) {
+        await mine()
+      }
+      expect(await proofs.isProofRequired(slotId)).to.be.true
+    })
+
     it("requires no proofs in the start period", async function () {
       const startPeriod = Math.floor((await currentTime()) / period)
       const probability = 1