diff --git a/CHANGES b/CHANGES
index cca82fa..127c273 100644
--- a/CHANGES
+++ b/CHANGES
@@ -2,6 +2,8 @@
   array_allocate no longer truncates the array
   array_get now not only checks whether the element fits in the
     allocates space, it also needs to be in the initialized space.
+  add -D_REENTRANT to CFLAGS so libowfat can be used in multi-threaded
+    programs
 
 0.24:
   fix scan_to_sa (Tim Lorenz)
diff --git a/GNUmakefile b/GNUmakefile
index b60fdca..2c9d1e7 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -20,6 +20,8 @@ CFLAGS=-pipe -W -Wall -O2 -fomit-frame-pointer
 
 # CFLAGS += -fstrict-aliasing -Wstrict-aliasing=2
 
+CFLAGS += -D_REENTRANT
+
 # startrip
 ifneq ($(DEBUG),)
 CFLAGS=-pipe -Wall -g
diff --git a/Makefile b/Makefile
index 6a05f9b..8a99c97 100644
--- a/Makefile
+++ b/Makefile
@@ -19,6 +19,8 @@ CC=gcc
 CFLAGS=-pipe -W -Wall -O2 -fomit-frame-pointer
 #CFLAGS=-pipe -Os -march=pentiumpro -mcpu=pentiumpro -fomit-frame-pointer -fschedule-insns2 -Wall
 
+CFLAGS += -D_REENTRANT
+
 # CFLAGS += -fstrict-aliasing -Wstrict-aliasing=2
 
 array_allocate.o: array/array_allocate.c safemult.h uint16.h \
diff --git a/array.h b/array.h
index 658d7e5..953ce14 100644
--- a/array.h
+++ b/array.h
@@ -2,7 +2,6 @@
 #define ARRAY_H
 
 #include "uint64.h"
-#include <errno.h>
 
 typedef struct {
   char* p;
diff --git a/io/io_fd.c b/io/io_fd.c
index b707c40..e361ddf 100644
--- a/io/io_fd.c
+++ b/io/io_fd.c
@@ -88,6 +88,10 @@ int io_fd(int64 d) {
           sigprocmask(SIG_BLOCK,&io_ss,0)==0)
 	io_waitmode=_SIGIO;
     }
+#endif
+#ifdef __MINGW32__
+    io_comport=CreateIoCompletionPort(INVALID_HANDLE_VALUE,NULL,0,1);
+    if (io_comport) io_waitmode=COMPLETIONPORT;
 #endif
   }
 #if defined(HAVE_SIGIO)
diff --git a/io/io_mmapwritefile.c b/io/io_mmapwritefile.c
index a1a50d5..1fdd7f9 100644
--- a/io/io_mmapwritefile.c
+++ b/io/io_mmapwritefile.c
@@ -6,6 +6,7 @@
 #include <windows.h>
 #else
 #include <sys/mman.h>
+#include <errno.h>
 #endif
 
 #define BUFSIZE 16384
diff --git a/io/io_sendfile.c b/io/io_sendfile.c
index 92ea954..5c3b20a 100644
--- a/io/io_sendfile.c
+++ b/io/io_sendfile.c
@@ -3,6 +3,7 @@
 #include "io_internal.h"
 #include "havebsdsf.h"
 #include "havesendfile.h"
+#include <errno.h>
 
 #if defined(HAVE_BSDSENDFILE)
 #define SENDFILE 1
diff --git a/io_internal.h b/io_internal.h
index 8b67dd7..34411f7 100644
--- a/io_internal.h
+++ b/io_internal.h
@@ -56,6 +56,9 @@ extern enum __io_waitmode {
 #ifdef HAVE_DEVPOLL
   ,DEVPOLL
 #endif
+#ifdef __MINGW32__
+  ,COMPLETIONPORT
+#endif
 } io_waitmode;
 
 #if defined(HAVE_KQUEUE) || defined(HAVE_EPOLL) || defined(HAVE_DEVPOLL)