diff --git a/Example.hs b/Example.hs
--- a/Example.hs
+++ b/Example.hs
@@ -3,7 +3,7 @@
 module Example where
 
 import           Control.Monad.IO.Class                         (liftIO)
-import           System.Metrics.Prometheus.Concurrent.Http      (serveHttpTextMetricsT)
+import           System.Metrics.Prometheus.Http.Scrape          (serveHttpTextMetricsT)
 import           System.Metrics.Prometheus.Concurrent.RegistryT
 import           System.Metrics.Prometheus.Metric.Counter       (inc)
 import           System.Metrics.Prometheus.MetricId
diff --git a/README.md b/README.md
--- a/README.md
+++ b/README.md
@@ -17,7 +17,7 @@
 module Example where
 
 import           Control.Monad.IO.Class                         (liftIO)
-import           System.Metrics.Prometheus.Concurrent.Http      (serveHttpTextMetricsT)
+import           System.Metrics.Prometheus.Http.Scrape          (serveHttpTextMetricsT)
 import           System.Metrics.Prometheus.Concurrent.RegistryT
 import           System.Metrics.Prometheus.Metric.Counter       (inc)
 import           System.Metrics.Prometheus.MetricId
diff --git a/prometheus.cabal b/prometheus.cabal
--- a/prometheus.cabal
+++ b/prometheus.cabal
@@ -1,5 +1,5 @@
 name:                prometheus
-version:             2.1.1
+version:             2.1.2
 synopsis:            Prometheus Haskell Client
 homepage:            http://github.com/bitnomial/prometheus
 bug-reports:         http://github.com/bitnomial/prometheus/issues
@@ -26,7 +26,7 @@
   > module Example where
   >
   > import           Control.Monad.IO.Class                         (liftIO)
-  > import           System.Metrics.Prometheus.Concurrent.Http      (serveHttpTextMetricsT)
+  > import           System.Metrics.Prometheus.Http.Scrape          (serveHttpTextMetricsT)
   > import           System.Metrics.Prometheus.Concurrent.RegistryT
   > import           System.Metrics.Prometheus.Metric.Counter       (inc)
   > import           System.Metrics.Prometheus.MetricId
@@ -77,10 +77,10 @@
                  , System.Metrics.Prometheus.Registry
                  , System.Metrics.Prometheus.RegistryT
 
-  build-depends: base           >= 4.7  && < 4.13
+  build-depends: base           >= 4.9  && < 4.13
                , atomic-primops >= 0.8  && < 0.9
                , bytestring     >= 0.10 && < 0.11
-               , containers     >= 0.5  && < 0.6
+               , containers     >= 0.5  && < 0.7
                , http-client    >= 0.4  && < 0.6
                , http-types     >= 0.8  && < 0.13
                , network-uri    >= 2.5  && < 2.7
diff --git a/src/System/Metrics/Prometheus/Metric/Histogram.hs b/src/System/Metrics/Prometheus/Metric/Histogram.hs
--- a/src/System/Metrics/Prometheus/Metric/Histogram.hs
+++ b/src/System/Metrics/Prometheus/Metric/Histogram.hs
@@ -17,8 +17,8 @@
 import           Data.Bool           (bool)
 import           Data.IORef          (IORef, atomicModifyIORef', newIORef,
                                       readIORef)
-import           Data.Map            (Map)
-import qualified Data.Map            as Map
+import           Data.Map.Strict     (Map)
+import qualified Data.Map.Strict     as Map
 
 
 newtype Histogram = Histogram { unHistogram :: IORef HistogramSample }
@@ -30,9 +30,9 @@
 
 data HistogramSample =
     HistogramSample
-    { histBuckets :: Buckets
-    , histSum     :: Double
-    , histCount   :: Int
+    { histBuckets :: !Buckets
+    , histSum     :: !Double
+    , histCount   :: !Int
     }
 
 
diff --git a/src/System/Metrics/Prometheus/Metric/Summary.hs b/src/System/Metrics/Prometheus/Metric/Summary.hs
--- a/src/System/Metrics/Prometheus/Metric/Summary.hs
+++ b/src/System/Metrics/Prometheus/Metric/Summary.hs
@@ -1,10 +1,10 @@
 module System.Metrics.Prometheus.Metric.Summary where
 
-import           Data.Map (Map)
+import           Data.Map.Strict (Map)
 
 data SummarySample =
     SummarySample
-    { sumQuantiles :: Map Double Int
-    , sumSum       :: Int
-    , sumCount     :: Int
+    { sumQuantiles :: !(Map Double Int)
+    , sumSum       :: !Int
+    , sumCount     :: !Int
     }