diff --git a/contracts/MedianOracle.sol b/contracts/MedianOracle.sol
index bce5046..98c00a6 100644
--- a/contracts/MedianOracle.sol
+++ b/contracts/MedianOracle.sol
@@ -120,13 +120,18 @@ contract MedianOracle is Ownable, IOracle {
         Report[2] storage reports = providerReports[providerAddress];
         uint256[2] memory timestamps = [reports[0].timestamp, reports[1].timestamp];
 
+        // Checks that this providerAddress is already whitelisted
         require(timestamps[0] > 0);
 
         uint8 index_recent = timestamps[0] >= timestamps[1] ? 0 : 1;
         uint8 index_past = 1 - index_recent;
 
+        uint256 minValidTimestamp = now.sub(reportExpirationTimeSec);
+        uint256 maxValidTimestamp = now.sub(reportDelaySec);
+
         // Check that the push is not too soon after the last one.
-        require(timestamps[index_recent].add(reportDelaySec) <= now);
+        require(timestamps[index_past] < minValidTimestamp ||
+            timestamps[index_recent] <= maxValidTimestamp);
 
         reports[index_past].timestamp = now;
         reports[index_past].payload = payload;
@@ -140,6 +145,7 @@ contract MedianOracle is Ownable, IOracle {
     function purgeReports() external
     {
         address providerAddress = msg.sender;
+        // Check that this providerAddress is already whitelisted
         require (providerReports[providerAddress][0].timestamp > 0);
         providerReports[providerAddress][0].timestamp=1;
         providerReports[providerAddress][1].timestamp=1;
diff --git a/test/unit/median_oracle.js b/test/unit/median_oracle.js
index c51fcc0..500c97e 100644
--- a/test/unit/median_oracle.js
+++ b/test/unit/median_oracle.js
@@ -69,6 +69,15 @@ contract('MedianOracle:addProvider', async function (accounts) {
   });
 });
 
+// TODO(naguib): Add test scenarios for:
+// Reported rates (ordered by time) are r1, r2. The new rate is r.
+//   r2 < minValidTimestamp
+//   r1 < minValidTimestamp < r2 < maxValidTimestamp
+//   minValidTimestamp < r1 < r2 < maxValidTimestamp
+//   r1 < minValidTimestamp < maxValidTimestamp < r2
+//   minValidTimestamp < r1 < maxValidTimestamp < r2
+//   maxValidTimestamp < r1
+
 contract('MedianOracle:pushReport', async function (accounts) {
   before(async function () {
     await setupContractsAndAccounts(accounts);
@@ -77,7 +86,8 @@ contract('MedianOracle:pushReport', async function (accounts) {
     expect(await chain.isEthException(oracle.pushReport(1000000000000000000, { from: A }))).to.be.true;
     oracle.addProvider(A, { from: deployer });
     r = await oracle.pushReport(1000000000000000000, { from: A });
-    // should fail if reportDelaySec did not pass since the previous push
+    r = await oracle.pushReport(1000000000000000000, { from: A });
+    // should fail if push is too early
     expect(await chain.isEthException(oracle.pushReport(1000000000000000000, { from: A }))).to.be.true;
   });
   it('should emit ProviderReportPushed message', async function () {