diff --git a/contracts/StorageContract.sol b/contracts/StorageContract.sol
index fd77b98..54e09da 100644
--- a/contracts/StorageContract.sol
+++ b/contracts/StorageContract.sol
@@ -14,6 +14,7 @@ contract StorageContract {
   uint public immutable proofMarker; // indicates when a proof is required
 
   mapping(uint => bool) proofReceived; // whether proof for a block was received
+  uint public missingProofs;
 
   constructor(uint _duration,
               uint _size,
@@ -111,14 +112,22 @@ contract StorageContract {
     return hash != 0 && uint(hash) % proofPeriod == proofMarker;
   }
 
+  function isProofTimedOut(uint blocknumber) internal view returns (bool) {
+    return block.number >= blocknumber + proofTimeout;
+  }
+
   function submitProof(uint blocknumber, bool proof) public {
     require(proof, "Invalid proof"); // TODO: replace bool by actual proof
     require(isProofRequired(blocknumber), "No proof required for this block");
-    require(
-      block.number < blocknumber + proofTimeout,
-      "Proof not allowed after timeout"
-    );
+    require(!isProofTimedOut(blocknumber), "Proof not allowed after timeout");
     require(!proofReceived[blocknumber], "Proof already submitted");
     proofReceived[blocknumber] = true;
   }
+
+  function markProofAsMissing(uint blocknumber) public {
+    require(isProofTimedOut(blocknumber), "Proof has not timed out yet");
+    require(!proofReceived[blocknumber], "Proof was submitted, not missing");
+    require(isProofRequired(blocknumber), "Proof was not required");
+    missingProofs += 1;
+  }
 }
diff --git a/test/StorageContract.test.js b/test/StorageContract.test.js
index 59b23af..030d373 100644
--- a/test/StorageContract.test.js
+++ b/test/StorageContract.test.js
@@ -174,6 +174,12 @@ describe("Storage Contract", function () {
       }
     }
 
+    async function mineUntilProofTimeout() {
+      for (let i=0; i<proofTimeout; i++) {
+        mineBlock()
+      }
+    }
+
     beforeEach(async function () {
       contract = await StorageContract.deploy(
         duration,
@@ -238,9 +244,7 @@ describe("Storage Contract", function () {
     it("fails proof submission when proof is too late", async function () {
       await mineUntilProofIsRequired()
       let blocknumber = await minedBlockNumber()
-      for (let i=0; i<proofTimeout; i++) {
-        mineBlock()
-      }
+      await mineUntilProofTimeout()
       await expect(
         contract.submitProof(blocknumber, true)
       ).to.be.revertedWith("Proof not allowed after timeout")
@@ -254,13 +258,51 @@ describe("Storage Contract", function () {
         contract.submitProof(blocknumber, true)
       ).to.be.revertedWith("Proof already submitted")
     })
+
+    it("marks a proof as missing", async function () {
+      expect(await contract.missingProofs()).to.equal(0)
+      await mineUntilProofIsRequired()
+      let blocknumber = await minedBlockNumber()
+      await mineUntilProofTimeout()
+      await contract.markProofAsMissing(blocknumber)
+      expect(await contract.missingProofs()).to.equal(1)
+    })
+
+    it("does not mark a proof as missing before timeout", async function () {
+      await mineUntilProofIsRequired()
+      let blocknumber = await minedBlockNumber()
+      await mineBlock()
+      await expect(
+        contract.markProofAsMissing(blocknumber)
+      ).to.be.revertedWith("Proof has not timed out yet")
+    })
+
+    it("does not mark a submitted proof as missing", async function () {
+      await mineUntilProofIsRequired()
+      let blocknumber = await minedBlockNumber()
+      await contract.submitProof(blocknumber, true)
+      await mineUntilProofTimeout()
+      await expect(
+        contract.markProofAsMissing(blocknumber)
+      ).to.be.revertedWith("Proof was submitted, not missing")
+    })
+
+    it("does not mark proof as missing when not required", async function () {
+      while (await contract.isProofRequired(await minedBlockNumber())) {
+        mineBlock()
+      }
+      let blocknumber = await minedBlockNumber()
+      await mineUntilProofTimeout()
+      await expect(
+        contract.markProofAsMissing(blocknumber)
+      ).to.be.revertedWith("Proof was not required")
+    })
   })
 })
 
 // TODO: implement checking of actual proofs of storage, instead of dummy bool
 // TODO: payment on constructor
 // TODO: contract start and timeout
-// TODO: missed proofs
 // TODO: only allow proofs after start of contract
 // TODO: payout
 // TODO: stake