diff --git a/Network/Sendfile/BSD.hsc b/Network/Sendfile/BSD.hsc
--- a/Network/Sendfile/BSD.hsc
+++ b/Network/Sendfile/BSD.hsc
@@ -43,7 +43,7 @@
 sendfile sock path range hook = bracket setup teardown $ \fd ->
     sendfileFd sock fd range hook
   where
-    setup = openFd path ReadOnly Nothing defaultFileFlags
+    setup = openFd path ReadOnly Nothing defaultFileFlags{nonBlock=True}
     teardown = closeFd
 
 -- |
@@ -104,7 +104,7 @@
 sendfileWithHeader sock path range hook hdr =
     bracket setup teardown $ \fd -> sendfileFdWithHeader sock fd range hook hdr
   where
-    setup = openFd path ReadOnly Nothing defaultFileFlags
+    setup = openFd path ReadOnly Nothing defaultFileFlags{nonBlock=True}
     teardown = closeFd
 
 -- |
diff --git a/Network/Sendfile/Linux.hsc b/Network/Sendfile/Linux.hsc
--- a/Network/Sendfile/Linux.hsc
+++ b/Network/Sendfile/Linux.hsc
@@ -62,7 +62,7 @@
 sendfile sock path range hook = bracket setup teardown $ \fd ->
     sendfileFd sock fd range hook
   where
-    setup = openFd path ReadOnly Nothing defaultFileFlags
+    setup = openFd path ReadOnly Nothing defaultFileFlags{nonBlock=True}
     teardown = closeFd
 
 -- |
diff --git a/simple-sendfile.cabal b/simple-sendfile.cabal
--- a/simple-sendfile.cabal
+++ b/simple-sendfile.cabal
@@ -1,5 +1,5 @@
 Name:                   simple-sendfile
-Version:                0.2.20
+Version:                0.2.21
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3