diff --git a/ethereum/contracts/Work1.sol b/ethereum/contracts/Work1.sol
index db094d6..8c1fab8 100644
--- a/ethereum/contracts/Work1.sol
+++ b/ethereum/contracts/Work1.sol
@@ -70,7 +70,13 @@ contract Work1 is IAcceptAvailability {
             msg.sender == stake.worker,
             "Worker can only extend their own availability stake"
         );
-        stake.endTime = block.timestamp + duration;
+        require(!stake.reclaimed, "Stake has already been reclaimed");
+        require(!stake.assigned, "Stake has already been assigned work");
+        if (block.timestamp > stake.endTime) {
+            stake.endTime = block.timestamp + duration;
+        } else {
+            stake.endTime = stake.endTime + duration;
+        }
         emit AvailabilityStaked(stakeIndex);
     }
 
diff --git a/ethereum/test/Work1.js b/ethereum/test/Work1.js
index ddfe4cb..8e25c3f 100644
--- a/ethereum/test/Work1.js
+++ b/ethereum/test/Work1.js
@@ -103,6 +103,28 @@ describe('Work1', () => {
       await time.increase(STAKE_DURATION * 2);
       await expect(work1.connect(account2).extendAvailability(0, STAKE_DURATION)).to.be.revertedWith('Worker can only extend their own availability stake');
     });
+
+    it('should not be able to extend a stake that has been reclaimed', async () => {
+      await time.increase(STAKE_DURATION * 2);
+      await work1.reclaimAvailability(0);
+      await expect(work1.extendAvailability(0, STAKE_DURATION)).to.be.revertedWith('Stake has already been reclaimed');
+    });
+
+    it('extending a stake before expiration should increase the end time by the given duration', async () => {
+      await time.increase(STAKE_DURATION / 2);
+      await work1.extendAvailability(0, STAKE_DURATION * 2);
+      const expectedEndTime = await time.latest() + 2.5 * STAKE_DURATION;
+      const stake = await work1.stakes(0);
+      expect(stake.endTime).to.be.within(expectedEndTime - 1, expectedEndTime);
+    });
+
+    it('extending a stake after expiration should restart the stake for the given duration', async () => {
+      await time.increase(STAKE_DURATION * 2);
+      await work1.extendAvailability(0, STAKE_DURATION * 2);
+      const expectedEndTime = await time.latest() + STAKE_DURATION * 2;
+      const stake = await work1.stakes(0);
+      expect(stake.endTime).to.be.within(expectedEndTime - 1, expectedEndTime);
+    });
   });
 
   describe('Request and assign work', () => {
@@ -163,6 +185,16 @@ describe('Work1', () => {
       await expect(requestWork()).to.emit(work1, 'WorkAssigned').withArgs(account1, 0);
       await expect(requestWork()).to.be.revertedWith('No available worker stakes');
     });
+
+    it('should not be able to extend a stake that has been assigned work', async () => {
+      const {
+        dao, work1, account2,
+      } = await loadFixture(deploy);
+      await dao.stakeAvailability(work1.target, 50, STAKE_DURATION);
+      await work1.connect(account2).requestWork({ value: WORK1_PRICE });
+      await time.increase(STAKE_DURATION * 2);
+      await expect(work1.extendAvailability(0, STAKE_DURATION)).to.be.revertedWith('Stake has already been assigned work');
+    });
   });
 
   describe('Work evidence and approval/disapproval', () => {