diff --git a/libraries/base/GHC/Event/Windows.hsc b/libraries/base/GHC/Event/Windows.hsc
index 1d81819e2f06e16d5a1f8846ab927e1fce203f68..ea2c51053a0687b811a4b0110f50739a309f38d9 100644
--- a/libraries/base/GHC/Event/Windows.hsc
+++ b/libraries/base/GHC/Event/Windows.hsc
@@ -668,7 +668,7 @@ withOverlappedEx mgr fname h offset startCB completionCB = do
                         -- the pointer.
                         debugIO $ "## Waiting for cancellation record... "
                         _ <- FFI.getOverlappedResult h lpol True
-                        oldDataPtr <- exchangePtr ptr_lpol nullReq
+                        oldDataPtr <- I.exchangePtr ptr_lpol nullReq
                         when (oldDataPtr == cdData) $
                           do reqs1 <- removeRequest
                              debugIO $ "-1.. " ++ show reqs1 ++ " requests queued after error."