diff --git a/src/mzscheme/src/env.c b/src/mzscheme/src/env.c
index 7d8497c851..d489c62a37 100644
--- a/src/mzscheme/src/env.c
+++ b/src/mzscheme/src/env.c
@@ -442,6 +442,7 @@ static Scheme_Env *place_instance_init_post_kernel() {
   scheme_init_stx_places();
   scheme_init_sema_places();
   scheme_init_gmp_places();
+  scheme_alloc_global_fdset();
 
   env = scheme_make_empty_env();
   scheme_set_param(scheme_current_config(), MZCONFIG_ENV, (Scheme_Object *)env); 
diff --git a/src/mzscheme/src/network.c b/src/mzscheme/src/network.c
index d2398996e1..90adde8bfb 100644
--- a/src/mzscheme/src/network.c
+++ b/src/mzscheme/src/network.c
@@ -59,7 +59,6 @@ static int mzerrno = 0;
 #else
 # include <errno.h>
 #endif
-#include "schfd.h"
 
 #ifdef USE_UNIX_SOCKETS_TCP
 # include <netinet/in.h>
@@ -93,6 +92,8 @@ struct SOCKADDR_IN {
 extern int scheme_stupid_windows_machine;
 #endif
 
+#include "schfd.h"
+
 #define TCP_BUFFER_SIZE 4096
 
 #ifdef USE_UNIX_SOCKETS_TCP
@@ -157,13 +158,19 @@ typedef struct Scheme_UDP {
 
 #if defined(WINDOWS_PROCESSES) || defined(WINDOWS_FILE_HANDLES)
 # define DECL_OS_FDSET(n) fd_set n[1]
-# define INIT_DECL_OS_FDSET(n) /* empty */
+# define INIT_DECL_OS_FDSET(r, w, e) /* empty */
+# define INIT_DECL_OS_RD_FDSET(r) /* empty */
+# define INIT_DECL_OS_WR_FDSET(r) /* empty */
+# define INIT_DECL_OS_ER_FDSET(r) /* empty */
 # define MZ_OS_FD_ZERO(p) FD_ZERO(p)
 # define MZ_OS_FD_SET(n, p) FD_SET(n, p)
 # define MZ_OS_FD_CLR(n, p) FD_CLR(n, p)
 #else
 # define DECL_OS_FDSET(n) DECL_FDSET(n, 1)
-# define INIT_DECL_OS_FDSET(n) INIT_DECL_FDSET(n, 1)
+# define INIT_DECL_OS_FDSET(r, w, e) INIT_DECL_FDSET(r, w, e)
+# define INIT_DECL_OS_RD_FDSET(r) INIT_DECL_RD_FDSET(r)
+# define INIT_DECL_OS_WR_FDSET(r) INIT_DECL_WR_FDSET(r)
+# define INIT_DECL_OS_ER_FDSET(r) INIT_DECL_ER_FDSET(r)
 # define MZ_OS_FD_ZERO(p) MZ_FD_ZERO(p)
 # define MZ_OS_FD_SET(n, p) MZ_FD_SET(n, p)
 # define MZ_OS_FD_CLR(n, p) MZ_FD_CLR(n, p)
@@ -816,8 +823,8 @@ static int tcp_check_accept(Scheme_Object *_listener)
   struct timeval time = {0, 0};
   int sr, i;
 
-  INIT_DECL_OS_FDSET(readfds);
-  INIT_DECL_OS_FDSET(exnfds);
+  INIT_DECL_OS_RD_FDSET(readfds);
+  INIT_DECL_OS_ER_FDSET(exnfds);
 
   if (LISTENER_WAS_CLOSED(listener))
     return 1;
@@ -880,8 +887,8 @@ static int tcp_check_connect(Scheme_Object *connector_p)
   struct timeval time = {0, 0};
   int sr;
 
-  INIT_DECL_OS_FDSET(writefds);
-  INIT_DECL_OS_FDSET(exnfds);
+  INIT_DECL_OS_WR_FDSET(writefds);
+  INIT_DECL_OS_ER_FDSET(exnfds);
 
   s = *(tcp_t *)connector_p;
 
@@ -935,8 +942,8 @@ static int tcp_check_write(Scheme_Object *port)
     struct timeval time = {0, 0};
     int sr;
     
-    INIT_DECL_OS_FDSET(writefds);
-    INIT_DECL_OS_FDSET(exnfds);
+    INIT_DECL_OS_WR_FDSET(writefds);
+    INIT_DECL_OS_ER_FDSET(exnfds);
     
     s = data->tcp;
     
@@ -1034,8 +1041,8 @@ static int tcp_byte_ready (Scheme_Input_Port *port)
   DECL_OS_FDSET(exfds);
   struct timeval time = {0, 0};
 
-  INIT_DECL_OS_FDSET(readfds);
-  INIT_DECL_OS_FDSET(exfds);
+  INIT_DECL_OS_RD_FDSET(readfds);
+  INIT_DECL_OS_ER_FDSET(exfds);
 #endif
 
   if (port->closed)
@@ -2807,8 +2814,8 @@ static int udp_check_send(Scheme_Object *_udp)
     struct timeval time = {0, 0};
     int sr;
     
-    INIT_DECL_OS_FDSET(writefds);
-    INIT_DECL_OS_FDSET(exnfds);
+    INIT_DECL_OS_WR_FDSET(writefds);
+    INIT_DECL_OS_ER_FDSET(exnfds);
     
     MZ_OS_FD_ZERO(writefds);
     MZ_OS_FD_SET(udp->s, writefds);
@@ -3039,8 +3046,8 @@ static int udp_check_recv(Scheme_Object *_udp)
     struct timeval time = {0, 0};
     int sr;
     
-    INIT_DECL_OS_FDSET(readfds);
-    INIT_DECL_OS_FDSET(exnfds);
+    INIT_DECL_OS_RD_FDSET(readfds);
+    INIT_DECL_OS_ER_FDSET(exnfds);
     
     MZ_OS_FD_ZERO(readfds);
     MZ_OS_FD_SET(udp->s, readfds);
diff --git a/src/mzscheme/src/port.c b/src/mzscheme/src/port.c
index 92ed9e5e63..83cd58d4ce 100644
--- a/src/mzscheme/src/port.c
+++ b/src/mzscheme/src/port.c
@@ -77,7 +77,6 @@ static int mzerrno = 0;
 extern int osk_not_console; /* set by cmd-line flag */
 #endif
 #include <math.h> /* for fmod , used by default_sleep */
-#include "schfd.h"
 
 #ifndef MZ_BINARY
 # define MZ_BINARY 0
@@ -115,6 +114,8 @@ static void init_thread_memory();
 # define OS_THREAD_TYPE HANDLE
 #endif
 
+#include "schfd.h"
+
 #ifdef WINDOWS_FILE_HANDLES
 
 # define MZ_FDS
@@ -306,6 +307,8 @@ THREAD_LOCAL Scheme_Object *scheme_orig_stdout_port;
 THREAD_LOCAL Scheme_Object *scheme_orig_stderr_port;
 THREAD_LOCAL Scheme_Object *scheme_orig_stdin_port;
 
+THREAD_LOCAL fd_set *scheme_fd_set;
+
 Scheme_Object *(*scheme_make_stdin)(void) = NULL;
 Scheme_Object *(*scheme_make_stdout)(void) = NULL;
 Scheme_Object *(*scheme_make_stderr)(void) = NULL;
@@ -677,6 +680,13 @@ Scheme_Object * scheme_make_eof (void)
    Also implement special hooks for Windows "descriptors", like
    even queues and semaphores. */
 
+void scheme_alloc_global_fdset() {
+#ifdef USE_FAR_MZ_FDCALLS
+  REGISTER_SO(scheme_fd_set);
+  scheme_fd_set = scheme_alloc_fdset_array(3, 0);
+#endif
+}
+
 #ifdef USE_DYNAMIC_FDSET_SIZE
 static int dynamic_fd_size;
 
@@ -4925,8 +4935,8 @@ fd_byte_ready (Scheme_Input_Port *port)
     DECL_FDSET(exnfds, 1);
     struct timeval time = {0, 0};
 
-    INIT_DECL_FDSET(readfds, 1);
-    INIT_DECL_FDSET(exnfds, 1);
+    INIT_DECL_RD_FDSET(readfds);
+    INIT_DECL_ER_FDSET(exnfds);
 
     MZ_FD_ZERO(readfds);
     MZ_FD_ZERO(exnfds);
@@ -5938,8 +5948,8 @@ fd_write_ready (Scheme_Object *port)
     struct timeval time = {0, 0};
     int sr;
 
-    INIT_DECL_FDSET(writefds, 1);
-    INIT_DECL_FDSET(exnfds, 1);
+    INIT_DECL_WR_FDSET(writefds);
+    INIT_DECL_ER_FDSET(exnfds);
 
     MZ_FD_ZERO(writefds);
     MZ_FD_ZERO(exnfds);
@@ -8147,7 +8157,7 @@ static void default_sleep(float v, void *fds)
     if (external_event_fd) {
       DECL_FDSET(readfds, 1);
 
-      INIT_DECL_FDSET(readfds, 1);
+      INIT_DECL_RD_FDSET(readfds);
 
       MZ_FD_ZERO(readfds);
       MZ_FD_SET(external_event_fd, readfds);
diff --git a/src/mzscheme/src/schfd.h b/src/mzscheme/src/schfd.h
index 87d59517ef..b0d081b510 100644
--- a/src/mzscheme/src/schfd.h
+++ b/src/mzscheme/src/schfd.h
@@ -1,8 +1,19 @@
 
 #ifdef USE_FAR_MZ_FDCALLS
-# define DECL_FDSET(n, c) static fd_set *n
-# define INIT_DECL_FDSET(n, c) (n = (n ? (fd_set *)scheme_init_fdset_array(n, c) : (fd_set *)scheme_alloc_fdset_array(c, 1)))
+extern THREAD_LOCAL fd_set *scheme_fd_set;
+# define DECL_FDSET(n, c) fd_set *n
+# define INIT_DECL_FDSET(r, w, e) { \
+    r = MZ_GET_FDSET(scheme_fd_set, 0 ); \
+    w = MZ_GET_FDSET(scheme_fd_set, 1 ); \
+    e = MZ_GET_FDSET(scheme_fd_set, 2 ); \
+  }
+# define INIT_DECL_RD_FDSET(r) r = MZ_GET_FDSET(scheme_fd_set, 0 )
+# define INIT_DECL_WR_FDSET(r) r = MZ_GET_FDSET(scheme_fd_set, 1 )
+# define INIT_DECL_ER_FDSET(r) r = MZ_GET_FDSET(scheme_fd_set, 2 )
 #else
 # define DECL_FDSET(n, c) fd_set n[c]
-# define INIT_DECL_FDSET(n, c) /* empty */
+# define INIT_DECL_FDSET(r, w, e) /* empty */
+# define INIT_DECL_RD_FDSET(r) /* empty */
+# define INIT_DECL_WR_FDSET(r) /* empty */
+# define INIT_DECL_ER_FDSET(r) /* empty */
 #endif
diff --git a/src/mzscheme/src/schpriv.h b/src/mzscheme/src/schpriv.h
index 66ebd89acf..227fbe7b73 100644
--- a/src/mzscheme/src/schpriv.h
+++ b/src/mzscheme/src/schpriv.h
@@ -3119,6 +3119,7 @@ int scheme_is_user_port(Scheme_Object *port);
 int scheme_byte_ready_or_user_port_ready(Scheme_Object *p, Scheme_Schedule_Info *sinfo);
 
 int scheme_pipe_char_count(Scheme_Object *p);
+void scheme_alloc_global_fdset();
 
 #define CURRENT_INPUT_PORT(config) scheme_get_param(config, MZCONFIG_INPUT_PORT)
 #define CURRENT_OUTPUT_PORT(config) scheme_get_param(config, MZCONFIG_OUTPUT_PORT)
diff --git a/src/mzscheme/src/thread.c b/src/mzscheme/src/thread.c
index a7c70feef0..72b4258534 100644
--- a/src/mzscheme/src/thread.c
+++ b/src/mzscheme/src/thread.c
@@ -3531,7 +3531,7 @@ static int check_sleep(int need_activity, int sleep_now)
       scheme_notify_multithread(0);
     
 #if defined(USING_FDS)
-    INIT_DECL_FDSET(set, 3);
+    INIT_DECL_FDSET(set, set1, set2);
     set1 = (fd_set *) MZ_GET_FDSET(set, 1);
     set2 = (fd_set *) MZ_GET_FDSET(set, 2);