diff --git a/src/configure b/src/configure
index 5f78312c24..77300195f0 100755
--- a/src/configure
+++ b/src/configure
@@ -2402,6 +2402,8 @@ INSTALL_SETUP_FLAGS=
 
 STRIP_DEBUG=":"
 
+use_flag_pthread=yes
+
 ###### OSKit stuff #######
 
 if test "${enable_oskit}" = "yes" ; then
@@ -4103,6 +4105,7 @@ case "$host_os" in
     ;;
   nto-qnx*)
     enable_sgc=yes
+    use_flag_pthread=no
     LIBS="$LIBS -lsocket -Wl,--export-dynamic"
     ;;
   *)
@@ -8611,9 +8614,10 @@ fi
 ############### pthread ###################
 
 if test "${enable_pthread}" = "yes" ; then
-  # FIXME: the following two flags are GCC-specific:
-  PREFLAGS="$PREFLAGS -pthread"
-  LDFLAGS="$LDFLAGS -pthread"
+  if test "${use_flag_pthread}" = "yes" ; then
+    PREFLAGS="$PREFLAGS -pthread"
+    LDFLAGS="$LDFLAGS -pthread"
+  fi
 
 cat >>confdefs.h <<\_ACEOF
 #define USE_PTHREAD_INSTEAD_OF_ITIMER 1
diff --git a/src/racket/configure.ac b/src/racket/configure.ac
index 397f2c2089..7059091f8a 100644
--- a/src/racket/configure.ac
+++ b/src/racket/configure.ac
@@ -335,6 +335,8 @@ INSTALL_SETUP_FLAGS=
 
 STRIP_DEBUG=":"
 
+use_flag_pthread=yes
+
 ###### OSKit stuff #######
 
 if test "${enable_oskit}" = "yes" ; then
@@ -641,6 +643,7 @@ case "$host_os" in
     ;;
   nto-qnx*)
     enable_sgc=yes
+    use_flag_pthread=no
     LIBS="$LIBS -lsocket -Wl,--export-dynamic"
     ;;
   *)
@@ -1071,9 +1074,10 @@ fi
 ############### pthread ###################
 
 if test "${enable_pthread}" = "yes" ; then
-  # FIXME: the following two flags are GCC-specific:
-  PREFLAGS="$PREFLAGS -pthread"
-  LDFLAGS="$LDFLAGS -pthread"
+  if test "${use_flag_pthread}" = "yes" ; then
+    PREFLAGS="$PREFLAGS -pthread"
+    LDFLAGS="$LDFLAGS -pthread"
+  fi
   AC_DEFINE(USE_PTHREAD_INSTEAD_OF_ITIMER, 1, [Pthread timer enabled])
 
 [ msg="whether pthread_rwlock is available"   ]
diff --git a/src/racket/sconfig.h b/src/racket/sconfig.h
index 397fd77959..f37d8e40cc 100644
--- a/src/racket/sconfig.h
+++ b/src/racket/sconfig.h
@@ -965,6 +965,8 @@
 
 # define FLAGS_ALREADY_SET
 
+# define USE_DYNAMIC_FDSET_SIZE
+
 #if defined(i386)
 # define MZ_USE_JIT_I386
 # define MZ_JIT_USE_MPROTECT