fix warning on Windows

diff --git a/System/CPUTime.hsc b/System/CPUTime.hsc
index 5a7e696..f050a68 100644 (file)
--- a/System/CPUTime.hsc
+++ b/System/CPUTime.hsc
@@ -33,7 +33,9 @@ import CPUTime ( getCPUTime, cpuTimePrecision )
 #ifdef __GLASGOW_HASKELL__
 import Foreign hiding (unsafePerformIO)
 import Foreign.C
+#if !defined(CLK_TCK)
 import System.IO.Unsafe (unsafePerformIO)
+#endif
 
 #include "HsBaseConfig.h"