diff --git a/prometheus_resty_counter.lua b/prometheus_resty_counter.lua
index bbb0897..15e75db 100644
--- a/prometheus_resty_counter.lua
+++ b/prometheus_resty_counter.lua
@@ -97,10 +97,11 @@ function _M:incr(key, step, exptime)
   step = step or 1
   local value = self.increments[key]
   if value then
-    step = step + value.v
+    value.v = step + value.v
+    value.t = exptime
+  else
+    self.increments[key] = {v = step, t = exptime}
   end
-
-  self.increments[key] = {v = step, t = exptime}
   return true
 end
 
diff --git a/prometheus_test.lua b/prometheus_test.lua
index 5b63bd7..b080d2c 100644
--- a/prometheus_test.lua
+++ b/prometheus_test.lua
@@ -419,6 +419,65 @@ function TestPrometheus:testCounters()
   luaunit.assertEquals(self.dict:get('metric2{f2="v2",f1="v1"}'), 4)
   luaunit.assertEquals(ngx.logs, nil)
 end
+function TestPrometheus:testBufferedCounterExpiry()
+  local counter = self.p._counter
+  counter:incr("pending_nil", 1, 60)
+  counter:incr("pending_nil", 2)
+  counter:incr("pending_zero", 1, 60)
+  counter:incr("pending_zero", 0, 0)
+  counter:incr("pending_ttl", 1, 60)
+  counter:incr("pending_ttl", nil, 120)
+
+  local before = os.time()
+  luaunit.assertTrue(counter:sync())
+  luaunit.assertEquals(self.dict:get("pending_nil"), 3)
+  luaunit.assertEquals(self.dict:ttl("pending_nil"), 0)
+  luaunit.assertEquals(self.dict:get("pending_zero"), 1)
+  luaunit.assertEquals(self.dict:ttl("pending_zero"), 0)
+  luaunit.assertEquals(self.dict:get("pending_ttl"), 2)
+  local expiry = self.dict.dict.pending_ttl.expired
+  luaunit.assertTrue(expiry >= before + 120 and expiry <= os.time() + 120)
+
+  -- A nil expiry in the next batch leaves the shared dictionary's TTL intact.
+  counter:incr("pending_ttl", 0.5)
+  luaunit.assertTrue(counter:sync())
+  luaunit.assertEquals(self.dict:get("pending_ttl"), 2.5)
+  luaunit.assertEquals(self.dict.dict.pending_ttl.expired, expiry)
+
+  counter:incr("pending_ttl", 0, 0)
+  luaunit.assertTrue(counter:sync())
+  luaunit.assertEquals(self.dict:get("pending_ttl"), 2.5)
+  luaunit.assertEquals(self.dict:ttl("pending_ttl"), 0)
+  luaunit.assertEquals(ngx.logs, nil)
+end
+function TestPrometheus:testBufferedMetricsAcrossSyncs()
+  self.counter1:inc()
+  self.counter1:inc(4)
+  self.hist1:observe(0.25)
+  self.hist1:observe(0.5)
+  self.hist1:observe(-0.125)
+
+  luaunit.assertTrue(self.p._counter:sync())
+  luaunit.assertTrue(self.p._counter:sync())
+  luaunit.assertEquals(self.dict:get("metric1"), 5)
+  luaunit.assertEquals(self.dict:get("l1_count"), 3)
+  luaunit.assertEquals(self.dict:get("l1_sum"), 0.625)
+  luaunit.assertEquals(self.dict:get('l1_bucket{le="00.005"}'), 1)
+  luaunit.assertEquals(self.dict:get('l1_bucket{le="00.500"}'), 3)
+  luaunit.assertEquals(self.dict:get('l1_bucket{le="Inf"}'), 3)
+
+  self.counter1:inc(0)
+  self.counter1:inc()
+  self.hist1:observe(0.125)
+  luaunit.assertTrue(self.p._counter:sync())
+  luaunit.assertEquals(self.dict:get("metric1"), 6)
+  luaunit.assertEquals(self.dict:get("l1_count"), 4)
+  luaunit.assertEquals(self.dict:get("l1_sum"), 0.75)
+  luaunit.assertEquals(self.dict:get('l1_bucket{le="00.005"}'), 1)
+  luaunit.assertEquals(self.dict:get('l1_bucket{le="00.500"}'), 4)
+  luaunit.assertEquals(self.dict:get('l1_bucket{le="Inf"}'), 4)
+  luaunit.assertEquals(ngx.logs, nil)
+end
 function TestPrometheus:testGaugeIncDec()
   self.gauge1:inc(-1)
   luaunit.assertEquals(self.dict:get("gauge1"), -1)