diff --git a/src/System/Metrics/Prometheus/Metric/Histogram.hs b/src/System/Metrics/Prometheus/Metric/Histogram.hs
index 438f01994..39a49c26a 100644
--- a/src/System/Metrics/Prometheus/Metric/Histogram.hs
+++ b/src/System/Metrics/Prometheus/Metric/Histogram.hs
@@ -50,7 +50,7 @@ new buckets = Histogram <$> newIORef empty
 observeAndSample :: Double -> Histogram -> IO HistogramSample
 observeAndSample x = flip atomicModifyIORef' update . unHistogram
   where
-    update histData = (hist' histData, histData)
+    update histData = (hist' histData, hist' histData)
     hist' histData =
         histData
             { histBuckets = updateBuckets x $ histBuckets histData