diff --git a/CHANGELOG.md b/CHANGELOG.md
index 47e091f..8d1a00c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,18 +4,30 @@ Change Log
 All notable changes to this project are noted in this file. This project adheres to [Semantic
 Versioning](http://semver.org/).
 
+0.4.1
+-----
+
+- Fixed issue (https://github.com/blue-yonder/azure-cost-mon/issues/12)
+  where the sum of multiple time series was numerically instable by
+  emitting only integer values. The instability resulted in more counter
+  resets within Prometheus than necessary, so that `increase` gave wrong
+  results!
+
+
 0.4.0
 -----
 
 - Use the `X-Prometheus-Scrape-Timeout-Seconds` header sent by
   prometheus to overwrite the internal request timeout default.
 
+
 0.3.1
 -----
 
 - Fixed the exporter to cope with the non-standard response for months
   without usage details.
 
+
 0.3.0
 -----
 
diff --git a/azure_costs_exporter/prometheus_collector.py b/azure_costs_exporter/prometheus_collector.py
index 927c48e..c728c82 100644
--- a/azure_costs_exporter/prometheus_collector.py
+++ b/azure_costs_exporter/prometheus_collector.py
@@ -106,6 +106,6 @@ def collect(self):
         groups = df.groupby(base_columns).sum()
 
         for name, value in groups.iterrows():
-            c.add_metric(name, value.ExtendedCost)
+            c.add_metric(name, int(round(value.ExtendedCost)))
 
         yield c
diff --git a/tests/data.py b/tests/data.py
index 113de08..c3b8ec1 100644
--- a/tests/data.py
+++ b/tests/data.py
@@ -11,7 +11,7 @@
   u'Date': u'03/01/2017',
   u'Day': 1,
   u'DepartmentName': u'Engineering',
-  u'ExtendedCost': 0.71,
+  u'ExtendedCost': 0.499222332425423563466,
   u'InstanceId': u'platform-vnet',
   u'MeterCategory': u'Virtual Network',
   u'MeterId': u'c90286c8-adf0-438e-a257-4468387df385',
@@ -42,7 +42,7 @@
   u'Date': u'03/01/2017',
   u'Day': 1,
   u'DepartmentName': u'Engineering',
-  u'ExtendedCost': 0.24,
+  u'ExtendedCost': 0.50000011123124314235234522345,
   u'InstanceId': u'/subscriptions/abc3455ac-3feg-2b3c5-abe4-ec1111111e6/resourceGroups/my-group/providers/Microsoft.Storage/storageAccounts/ss7q3264domxo',
   u'MeterCategory': u'Windows Azure Storage',
   u'MeterId': u'd23a5753-ff85-4ddf-af28-8cc5cf2d3882',
diff --git a/tests/test_collector.py b/tests/test_collector.py
index 6b4439f..166e829 100644
--- a/tests/test_collector.py
+++ b/tests/test_collector.py
@@ -57,8 +57,8 @@ def test_extract_metrics(api_url, enrollment):
     result = generate_latest(registry).decode('utf8').split('\n')
     assert len(result) == 5
 
-    expected_0 = 'costs{AccountName="platform",DepartmentName="engineering",MeterCategory="virtual network",MeterName="hours",MeterSubCategory="gateway hour",ResourceGroup="",SubscriptionName="production"} 0.71'
-    expected_1 = 'costs{AccountName="platform",DepartmentName="engineering",MeterCategory="windows azure storage",MeterName="standard io - page blob/disk (gb)",MeterSubCategory="locally redundant",ResourceGroup="my-group",SubscriptionName="production"} 0.24'
+    expected_0 = 'costs{AccountName="platform",DepartmentName="engineering",MeterCategory="virtual network",MeterName="hours",MeterSubCategory="gateway hour",ResourceGroup="",SubscriptionName="production"} 0.0'
+    expected_1 = 'costs{AccountName="platform",DepartmentName="engineering",MeterCategory="windows azure storage",MeterName="standard io - page blob/disk (gb)",MeterSubCategory="locally redundant",ResourceGroup="my-group",SubscriptionName="production"} 1.0'
 
     assert result[2] == expected_0
     assert result[3] == expected_1