diff --git a/config.h.in b/config.h.in
index 891ecae..efc2b5c 100644
--- a/config.h.in
+++ b/config.h.in
@@ -58,6 +58,9 @@
 /* Define to 1 if you have the `setenv' function. */
 #undef HAVE_SETENV
 
+/* Define to 1 if you have the `sigaltstack' function. */
+#undef HAVE_SIGALTSTACK
+
 /* Define to 1 if you have the <signal.h> header file. */
 #undef HAVE_SIGNAL_H
 
diff --git a/configure b/configure
index ed3916a..39d46a3 100755
--- a/configure
+++ b/configure
@@ -5537,9 +5537,11 @@ _ACEOF
 
 
 # remember to enable before release.
-# if (test $ac_cv_sizeof_void_p != 4); then
-#   AC_MSG_ERROR([Ikarus can only run in 32-bit mode.])
-# fi
+if (test $ac_cv_sizeof_void_p != 4); then
+  { { echo "$as_me:$LINENO: error: Ikarus can only run in 32-bit mode." >&5
+echo "$as_me: error: Ikarus can only run in 32-bit mode." >&2;}
+   { (exit 1); exit 1; }; }
+fi
 
 # Checks for libraries.
 { echo "$as_me:$LINENO: checking for library containing dlsym" >&5
@@ -8787,7 +8789,8 @@ fi
 
 
 
-for ac_func in bzero gettimeofday memmove memset munmap setenv sqrt strerror getaddrinfo
+
+for ac_func in sigaltstack bzero gettimeofday memmove memset munmap setenv sqrt strerror getaddrinfo
 do
 as_ac_var=`echo "ac_cv_func_$ac_func" | $as_tr_sh`
 { echo "$as_me:$LINENO: checking for $ac_func" >&5
diff --git a/configure.ac b/configure.ac
index 24ac877..66cef89 100644
--- a/configure.ac
+++ b/configure.ac
@@ -30,9 +30,9 @@ case "$target_os" in
 
 AC_CHECK_SIZEOF(void *)
 # remember to enable before release.
-# if (test $ac_cv_sizeof_void_p != 4); then
-#   AC_MSG_ERROR([Ikarus can only run in 32-bit mode.])
-# fi
+if (test $ac_cv_sizeof_void_p != 4); then
+  AC_MSG_ERROR([Ikarus can only run in 32-bit mode.])
+fi
 
 # Checks for libraries.
 AC_SEARCH_LIBS(dlsym, dl,, [AC_MSG_ERROR([Cannot find libdl])])
@@ -93,7 +93,7 @@ AC_FUNC_MMAP
 AC_FUNC_STAT
 AC_FUNC_STRFTIME
 AC_FUNC_STRTOD
-AC_CHECK_FUNCS([bzero gettimeofday memmove memset munmap setenv sqrt strerror getaddrinfo])
+AC_CHECK_FUNCS([sigaltstack bzero gettimeofday memmove memset munmap setenv sqrt strerror getaddrinfo])
 AC_CONFIG_HEADERS([config.h])
 AC_CONFIG_FILES(Makefile src/Makefile scheme/Makefile doc/Makefile lib/Makefile benchmarks/Makefile)
 AC_OUTPUT #(Makefile src/Makefile scheme/Makefile doc/Makefile)
diff --git a/scheme/last-revision b/scheme/last-revision
index 4d52c91..85ce150 100644
--- a/scheme/last-revision
+++ b/scheme/last-revision
@@ -1 +1 @@
-1331
+1332
diff --git a/scheme/run-tests.ss b/scheme/run-tests.ss
index 2c6dc64..fecc7a2 100755
--- a/scheme/run-tests.ss
+++ b/scheme/run-tests.ss
@@ -49,7 +49,6 @@
   (f 0 536870911000 536870911)
   (printf "[exact-integer-sqrt] Happy Happy Joy Joy\n"))
 
-
 (test-case-folding)
 (test-parse-flonums)
 (test-reader)
@@ -73,5 +72,5 @@
 (test-fxdiv0-and-mod0)
 (test-fxlength)
 (test-bitwise-bit-count)
-;(test-io)
+(test-io)
 (printf "Happy Happy Joy Joy\n")
diff --git a/src/ikarus-main.c b/src/ikarus-main.c
index 0c2d298..e8b9f3a 100644
--- a/src/ikarus-main.c
+++ b/src/ikarus-main.c
@@ -257,7 +257,7 @@ SYNOPSIS
 
 void
 register_alt_stack(){
-#ifndef __CYGWIN__
+#if HAVE_SIGALTSTACK
   char* stk = mmap(0, SIGSTKSZ, PROT_READ|PROT_WRITE|PROT_EXEC, 
                    MAP_PRIVATE|MAP_ANON, -1, 0);
 //  char* stk = ik_mmap(SIGSTKSZ);