diff --git a/ChangeLog.md b/ChangeLog.md
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -1,7 +1,10 @@
 # Changelog for experimenter
 
+Release 0.1.0.6 on 15.03.2021:
+    - Using withMVar instead of modifyMVar_
+
 Release 0.1.0.3 on 31.12.2020:
-  - Using username for LaTeX output
-  - Parameter tables are rendered using the tabularX to ensure the textwidth is not exceeded
-  - Nicer output for running the evaluations
+    - Using username for LaTeX output
+    - Parameter tables are rendered using the tabularX to ensure the textwidth is not exceeded
+    - Nicer output for running the evaluations
 ## Unreleased changes
diff --git a/experimenter.cabal b/experimenter.cabal
--- a/experimenter.cabal
+++ b/experimenter.cabal
@@ -4,10 +4,10 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 2dfd476c8b0f4da0340c035c0501e8087c0808ea9fba7aaec32f5527c7114c37
+-- hash: 2b9823aaa76e5b2c3460c6368bb8bacca57bd553f4e26daa4181b268f1fcf1bb
 
 name:           experimenter
-version:        0.1.0.4
+version:        0.1.0.6
 synopsis:       Perform scientific experiments stored in a DB, and generate reports.
 description:    Please see the README on GitHub at <https://github.com/schnecki/experimenter#readme>
 category:       Experiment
@@ -15,7 +15,7 @@
 bug-reports:    https://github.com/schnecki/experimenter/issues
 author:         Manuel Schneckenreither
 maintainer:     manuel.schneckenreither@uibk.ac.at
-copyright:      2020 Manuel Schneckenreither
+copyright:      2021 Manuel Schneckenreither
 license:        BSD3
 license-file:   LICENSE
 build-type:     Simple
diff --git a/src/Experimenter/Run.hs b/src/Experimenter/Run.hs
--- a/src/Experimenter/Run.hs
+++ b/src/Experimenter/Run.hs
@@ -754,10 +754,10 @@
 {-# NOINLINE splitSizeMVar #-}
 
 increaseSplitSize :: IO ()
-increaseSplitSize = liftIO $ modifyMVar_ splitSizeMVar (return . min 128000 . (*2))
+increaseSplitSize = liftIO $ void $ withMVar splitSizeMVar (return . min 128000 . (*2))
 
 decreaseSplitSize :: IO ()
-decreaseSplitSize = liftIO $ modifyMVar_ splitSizeMVar (return . max 500 . (`div` 2))
+decreaseSplitSize = liftIO $ void $ withMVar splitSizeMVar (return . max 500 . (`div` 2))
 
 getSplitSize :: IO Int
 getSplitSize = liftIO $ fromMaybe 5000 <$> tryReadMVar splitSizeMVar