diff --git a/lib/expiring_lock.rb b/lib/expiring_lock.rb
index 42c967a71dc67d9e0811a6155a39573b11cf8e1d..87692cc49e6c241010433ba9f1175c92bf1808a3 100644
--- a/lib/expiring_lock.rb
+++ b/lib/expiring_lock.rb
@@ -7,11 +7,12 @@ class ExpiringLock
 	end
 
 	def with(els=nil)
-		REDIS.exists(@name).then do |exists|
-			next els&.call if exists == 1
+		REDIS.set(@name, Time.now, "EX", @expiry, "NX").then do |result|
+			next els&.call if result.nil?
 
-			EMPromise.resolve(yield).then do |rval|
-				REDIS.setex(@name, @expiry, Time.now).then { rval }
+			EMPromise.resolve(yield).catch do |err|
+				REDIS.del(@name)
+				EMPromise.reject(err)
 			end
 		end
 	end
diff --git a/test/test_low_balance.rb b/test/test_low_balance.rb
index d639d44bb00709bbb849e86b7301db70f4732d33..b8625661ebc18e9ab184270cff8912592647180c 100644
--- a/test/test_low_balance.rb
+++ b/test/test_low_balance.rb
@@ -10,9 +10,9 @@ CustomerFinancials::REDIS = Minitest::Mock.new
 class LowBalanceTest < Minitest::Test
 	def test_for_locked
 		ExpiringLock::REDIS.expect(
-			:exists,
-			EMPromise.resolve(1),
-			["jmp_customer_low_balance-test"]
+			:set,
+			EMPromise.resolve(nil),
+			["jmp_customer_low_balance-test", Time, "EX", 604800, "NX"]
 		)
 		assert_kind_of LowBalance::Locked, LowBalance.for(customer).sync
 	end
@@ -20,20 +20,15 @@ class LowBalanceTest < Minitest::Test
 
 	def test_for_no_auto_top_up
 		ExpiringLock::REDIS.expect(
-			:exists,
-			EMPromise.resolve(0),
-			["jmp_customer_low_balance-test"]
+			:set,
+			EMPromise.resolve("OK"),
+			["jmp_customer_low_balance-test", Time, "EX", 604800, "NX"]
 		)
 		CustomerFinancials::REDIS.expect(
 			:smembers,
 			EMPromise.resolve([]),
 			["jmp_customer_btc_addresses-test"]
 		)
-		ExpiringLock::REDIS.expect(
-			:setex,
-			EMPromise.resolve(nil),
-			["jmp_customer_low_balance-test", 60 * 60 * 24 * 7, Time]
-		)
 		assert_kind_of(
 			LowBalance,
 			LowBalance.for(customer).sync
@@ -44,14 +39,9 @@ class LowBalanceTest < Minitest::Test
 
 	def test_for_auto_top_up
 		ExpiringLock::REDIS.expect(
-			:exists,
-			EMPromise.resolve(0),
-			["jmp_customer_low_balance-test"]
-		)
-		ExpiringLock::REDIS.expect(
-			:setex,
-			EMPromise.resolve(nil),
-			["jmp_customer_low_balance-test", 60 * 60 * 24 * 7, Time]
+			:set,
+			EMPromise.resolve("OK"),
+			["jmp_customer_low_balance-test", Time, "EX", 604800, "NX"]
 		)
 		assert_kind_of(
 			LowBalance::AutoTopUp,
diff --git a/test/test_web.rb b/test/test_web.rb
index aacabc5ea1dadecdc642e1102ac86548de3efcd3..ab2f5be42760bf3628b19134a4c9aad0438ff13b 100644
--- a/test/test_web.rb
+++ b/test/test_web.rb
@@ -125,9 +125,9 @@ class WebTest < Minitest::Test
 
 	def test_outbound_low_balance
 		ExpiringLock::REDIS.expect(
-			:exists,
-			EMPromise.resolve(1),
-			["jmp_customer_low_balance-customerid_low"]
+			:set,
+			EMPromise.resolve(nil),
+			["jmp_customer_low_balance-customerid_low", Time, "EX", 604800, "NX"]
 		)
 
 		post(
@@ -161,15 +161,9 @@ class WebTest < Minitest::Test
 		)
 
 		ExpiringLock::REDIS.expect(
-			:exists,
-			nil,
-			["jmp_customer_low_balance-customerid_topup"]
-		)
-
-		ExpiringLock::REDIS.expect(
-			:setex,
-			nil,
-			["jmp_customer_low_balance-customerid_topup", Integer, Time]
+			:set,
+			EMPromise.resolve("OK"),
+			["jmp_customer_low_balance-customerid_topup", Time, "EX", 604800, "NX"]
 		)
 
 		Customer::BLATHER.expect(
@@ -307,9 +301,9 @@ class WebTest < Minitest::Test
 
 	def test_inbound_low
 		ExpiringLock::REDIS.expect(
-			:exists,
-			EMPromise.resolve(1),
-			["jmp_customer_low_balance-customerid_low"]
+			:set,
+			EMPromise.resolve(nil),
+			["jmp_customer_low_balance-customerid_low", Time, "EX", 604800, "NX"]
 		)
 
 		post(