diff --git a/contracts/Exchanger.sol b/contracts/Exchanger.sol
index b6ae2e371d..d13b4ad14f 100644
--- a/contracts/Exchanger.sol
+++ b/contracts/Exchanger.sol
@@ -559,12 +559,6 @@ contract Exchanger is Owned, MixinSystemSettings, IExchanger {
         systemStatus().suspendSynth(currencyKey, CIRCUIT_BREAKER_SUSPENSION_REASON);
     }
 
-    // SIP-78
-    function setLastExchangeRateForSynth(bytes32 currencyKey, uint rate) external onlyExchangeRates {
-        require(rate > 0, "Rate must be above 0");
-        lastExchangeRate[currencyKey] = rate;
-    }
-
     // SIP-139
     function resetLastExchangeRate(bytes32[] calldata currencyKeys) external onlyOwner {
         (uint[] memory rates, bool anyRateInvalid) = exchangeRates().ratesAndInvalidForCurrencies(currencyKeys);
@@ -869,12 +863,6 @@ contract Exchanger is Owned, MixinSystemSettings, IExchanger {
         _;
     }
 
-    modifier onlyExchangeRates() {
-        IExchangeRates _exchangeRates = exchangeRates();
-        require(msg.sender == address(_exchangeRates), "Restricted to ExchangeRates");
-        _;
-    }
-
     // ========== EVENTS ==========
     event ExchangeEntryAppended(
         address indexed account,
diff --git a/contracts/PurgeableSynth.sol b/contracts/PurgeableSynth.sol
index 12f16983a2..278d8d09a2 100644
--- a/contracts/PurgeableSynth.sol
+++ b/contracts/PurgeableSynth.sol
@@ -50,8 +50,8 @@ contract PurgeableSynth is Synth {
 
         uint maxSupplyToPurge = exRates.effectiveValue("sUSD", maxSupplyToPurgeInUSD, currencyKey);
 
-        // Only allow purge when total supply is lte the max or the rate is frozen in ExchangeRates
-        require(totalSupply <= maxSupplyToPurge, "Cannot purge as total supply is above threshold and rate is not frozen.");
+        // Only allow purge when total supply is lte the max
+        require(totalSupply <= maxSupplyToPurge, "Cannot purge as total supply is above threshol.");
 
         for (uint i = 0; i < addresses.length; i++) {
             address holder = addresses[i];
diff --git a/contracts/interfaces/IExchanger.sol b/contracts/interfaces/IExchanger.sol
index 9e291bba6a..79dd6736b8 100644
--- a/contracts/interfaces/IExchanger.sol
+++ b/contracts/interfaces/IExchanger.sol
@@ -70,8 +70,6 @@ interface IExchanger {
             uint numEntries
         );
 
-    function setLastExchangeRateForSynth(bytes32 currencyKey, uint rate) external;
-
     function resetLastExchangeRate(bytes32[] calldata currencyKeys) external;
 
     function suspendSynthWithInvalidRate(bytes32 currencyKey) external;
diff --git a/test/contracts/Exchanger.spec.js b/test/contracts/Exchanger.spec.js
index ccf7044d53..518e3e61eb 100644
--- a/test/contracts/Exchanger.spec.js
+++ b/test/contracts/Exchanger.spec.js
@@ -2498,42 +2498,6 @@ contract('Exchanger (spec tests)', async accounts => {
 		});
 	};
 
-	const itSetsLastExchangeRateForSynth = () => {
-		describe('setLastExchangeRateForSynth() SIP-78', () => {
-			it('cannot be invoked by any user', async () => {
-				await onlyGivenAddressCanInvoke({
-					fnc: exchanger.setLastExchangeRateForSynth,
-					args: [sEUR, toUnit('100')],
-					accounts,
-					reason: 'Restricted to ExchangeRates',
-				});
-			});
-
-			describe('when ExchangeRates is spoofed using an account', () => {
-				beforeEach(async () => {
-					await resolver.importAddresses([toBytes32('ExchangeRates')], [account1], {
-						from: owner,
-					});
-					await exchanger.rebuildCache();
-				});
-				it('reverts when invoked by ExchangeRates with a 0 rate', async () => {
-					await assert.revert(
-						exchanger.setLastExchangeRateForSynth(sEUR, '0', { from: account1 }),
-						'Rate must be above 0'
-					);
-				});
-				describe('when invoked with a real rate by ExchangeRates', () => {
-					beforeEach(async () => {
-						await exchanger.setLastExchangeRateForSynth(sEUR, toUnit('1.9'), { from: account1 });
-					});
-					it('then lastExchangeRate is set for the synth', async () => {
-						assert.bnEqual(await exchanger.lastExchangeRate(sEUR), toUnit('1.9'));
-					});
-				});
-			});
-		});
-	};
-
 	const itPricesSpikeDeviation = () => {
 		describe('priceSpikeDeviation', () => {
 			const baseRate = 100;
@@ -3386,8 +3350,6 @@ contract('Exchanger (spec tests)', async accounts => {
 
 		itExchangesWithVirtual();
 
-		itSetsLastExchangeRateForSynth();
-
 		itPricesSpikeDeviation();
 
 		itSetsExchangeFeeRateForSynths();
@@ -3484,8 +3446,6 @@ contract('Exchanger (spec tests)', async accounts => {
 
 		itExchanges();
 
-		itSetsLastExchangeRateForSynth();
-
 		itPricesSpikeDeviation();
 
 		itSetsExchangeFeeRateForSynths();
diff --git a/test/contracts/ExchangerWithVirtualSynth.unit.js b/test/contracts/ExchangerWithVirtualSynth.unit.js
index 0a8a74e4f0..dee6b45bd2 100644
--- a/test/contracts/ExchangerWithVirtualSynth.unit.js
+++ b/test/contracts/ExchangerWithVirtualSynth.unit.js
@@ -25,13 +25,7 @@ contract('ExchangerWithVirtualSynth (unit tests)', async accounts => {
 		ensureOnlyExpectedMutativeFunctions({
 			abi: ExchangerWithVirtualSynth.abi,
 			ignoreParents: ['Owned', 'MixinResolver'],
-			expected: [
-				'exchange',
-				'resetLastExchangeRate',
-				'settle',
-				'suspendSynthWithInvalidRate',
-				'setLastExchangeRateForSynth',
-			],
+			expected: ['exchange', 'resetLastExchangeRate', 'settle', 'suspendSynthWithInvalidRate'],
 		});
 	});