diff --git a/test/hs/CMakeLists.txt b/test/hs/CMakeLists.txt
index a65339d..eaca3fa 100644
--- a/test/hs/CMakeLists.txt
+++ b/test/hs/CMakeLists.txt
@@ -61,10 +61,17 @@
     -odir=${CMAKE_CURRENT_BINARY_DIR}
     -hidir=${CMAKE_CURRENT_BINARY_DIR}
 )
+
+if (CMAKE_BUILD_TYPE STREQUAL "Debug")
+  set(hs_optimize -O0)
+else()
+  set(hs_optimize -O1)
+endif()
+
 add_custom_command(
     OUTPUT ${hs_crosstest_apps}
-    COMMAND ${GHC} ${hs_crosstest_args} ${CMAKE_CURRENT_SOURCE_DIR}/TestServer.hs -o TestServer
-    COMMAND ${GHC} ${hs_crosstest_args} ${CMAKE_CURRENT_SOURCE_DIR}/TestClient.hs -o TestClient
+    COMMAND ${GHC} ${hs_optimize} ${hs_crosstest_args} ${CMAKE_CURRENT_SOURCE_DIR}/TestServer.hs -o TestServer
+    COMMAND ${GHC} ${hs_optimize} ${hs_crosstest_args} ${CMAKE_CURRENT_SOURCE_DIR}/TestClient.hs -o TestClient
     DEPENDS ${hs_test_gen} haskell_library TestServer.hs TestClient.hs
 )
 add_custom_target(haskell_crosstest ALL
diff --git a/test/hs/TestClient.hs b/test/hs/TestClient.hs
index 057a560..0ebc0fd 100644
--- a/test/hs/TestClient.hs
+++ b/test/hs/TestClient.hs
@@ -29,7 +29,6 @@
 import Network.URI
 import System.Environment
 import System.Exit
-import System.Posix.Unistd
 import qualified Data.ByteString.Lazy as LBS
 import qualified Data.HashMap.Strict as Map
 import qualified Data.HashSet as Set
diff --git a/test/hs/TestServer.hs b/test/hs/TestServer.hs
index 90ec11e..4a88649 100755
--- a/test/hs/TestServer.hs
+++ b/test/hs/TestServer.hs
@@ -31,7 +31,7 @@
 import System.Environment
 import System.Exit
 import System.IO
-import System.Posix.Unistd
+import Control.Concurrent (threadDelay)
 import qualified System.IO as IO
 import qualified Data.HashMap.Strict as Map
 import qualified Data.HashSet as Set
@@ -241,7 +241,7 @@
 
   testOneway _ i = do
     System.IO.putStrLn $ "testOneway(" ++ show i ++ "): Sleeping..."
-    sleep (fromIntegral i)
+    threadDelay $ (fromIntegral i) * 1000000
     System.IO.putStrLn $ "testOneway(" ++ show i ++ "): done sleeping!"
 
 main :: IO ()