diff --git a/configure.ac b/configure.ac
index 1c3e637..85d65ff 100644
--- a/configure.ac
+++ b/configure.ac
@@ -6,7 +6,7 @@ AC_PREREQ(2.50)
 AC_CONFIG_AUX_DIR(autotools)
 AC_CANONICAL_SYSTEM
 
-AM_INIT_AUTOMAKE(elk, 3.99.4)
+AM_INIT_AUTOMAKE(elk, 3.99.5)
 AM_CONFIG_HEADER(config.h)
 
 AC_PROG_CC
@@ -85,21 +85,9 @@ AC_CHECK_HEADERS(termios.h sys/ioctl.h sys/filio.h)
 # set sysconf_open_max=yes.
 # If neither is set to "yes", an educated guess will be made.
 AC_CHECK_FUNCS(getdtablesize)
-AC_MSG_CHECKING(for _SC_OPEN_MAX in unistd.h)
-AC_EGREP_HEADER(_SC_OPEN_MAX, unistd.h, [
-  AC_MSG_RESULT(yes) AC_DEFINE(SC_OPEN_MAX_IN_UNISTD_H, 1, Define if <unistd.h> defines _SC_OPEN_MAX)
-],[
-  AC_MSG_RESULT(no)
-])
 
 # If POSIX-style pathconf() can be invoked with _PC_PATH_MAX to determine
 # the maximum pathname length, set pathconf_path_max=yes.
-AC_MSG_CHECKING(for _PC_PATH_MAX in unistd.h)
-AC_EGREP_HEADER(_PC_PATH_MAX, unistd.h, [
-  AC_MSG_RESULT(yes) AC_DEFINE(PC_PATH_MAX_IN_UNISTD_H, 1, Define if <unistd.h> defines _PC_PATH_MAX)
-],[
-  AC_MSG_RESULT(no)
-])
 
 # If the system page size can be determined by calling getpagesize()
 # set getpagesize=yes.
@@ -108,12 +96,6 @@ AC_EGREP_HEADER(_PC_PATH_MAX, unistd.h, [
 # These two variables are only required if the generational garbage
 # collector is used.
 AC_CHECK_FUNCS(getpagesize)
-AC_MSG_CHECKING(for _SC_PAGESIZE in unistd.h)
-AC_EGREP_HEADER(_SC_PAGESIZE, unistd.h, [
-  AC_MSG_RESULT(yes) AC_DEFINE(SC_PAGESIZE_IN_UNISTD_H, 1, Define if <unistd.h> defines _SC_PAGESIZE)
-],[
-  AC_MSG_RESULT(no)
-])
 
 # Set reliable_signals=bsd if your system supports BSD-style reliable
 # signals (has sigblock and related functions); set reliable_signals=posix
diff --git a/lib/unix/fdescr.c b/lib/unix/fdescr.c
index 8852995..54392ad 100644
--- a/lib/unix/fdescr.c
+++ b/lib/unix/fdescr.c
@@ -194,7 +194,7 @@ int Num_Filedescriptors() {
     ret = OPEN_MAX;
 #elif defined(HAVE_GETDTABLESIZE)
     ret = getdtablesize();
-#elif defined(SC_OPEN_MAX_IN_UNISTD_H)
+#elif defined(_SC_OPEN_MAX)
     static r;
     if (r == 0) {
         if ((r = sysconf(_SC_OPEN_MAX)) == -1)
diff --git a/src/heap-gen.c b/src/heap-gen.c
index 53acf13..7719429 100644
--- a/src/heap-gen.c
+++ b/src/heap-gen.c
@@ -42,7 +42,7 @@
 #if defined(MPROTECT_SIG) || defined(MPROTECT_MMAP)
 #  include <sys/mman.h>
 #endif
-#if defined(HAVE_GETPAGESIZE) || defined(SC_PAGESIZE_IN_UNISTD_H)
+#if defined(HAVE_UNISTD_H)
 #  include <unistd.h>
 #  if defined(_SC_PAGE_SIZE) && !defined(_SC_PAGESIZE)   /* Wrong in HP-UX */
 #    define _SC_PAGESIZE _SC_PAGE_SIZE
@@ -493,7 +493,7 @@ void Make_Heap (int size) {
      * then calculate the resulting number of heap pages.
      */
 
-#if defined(SC_PAGESIZE_IN_UNISTD_H)
+#if defined(_SC_PAGESIZE)
     if ((bytes_per_pp = sysconf (_SC_PAGESIZE)) == -1)
         Fatal_Error ("sysconf(_SC_PAGESIZE) failed; can't get pagesize");
 #elif defined(HAVE_GETPAGESIZE)
diff --git a/src/io.c b/src/io.c
index 1efc662..a66052f 100644
--- a/src/io.c
+++ b/src/io.c
@@ -40,7 +40,7 @@
 #include <sys/param.h>
 #include <sys/stat.h>
 
-#ifdef PC_PATH_MAX_IN_UNISTD_H
+#ifdef HAVE_UNISTD_H
 #  include <unistd.h>
 #endif
 
@@ -122,7 +122,7 @@ unsigned int Path_Max () {
     return PATH_MAX;
 #elif defined(MAXPATHLEN) /* 4.3 BSD */
     return MAXPATHLEN;
-#elif defined(PC_PATH_MAX_IN_UNISTD_H)
+#elif defined(_PC_PATH_MAX)
     static int r;
     if (r == 0) {
         if ((r = pathconf ("/", _PC_PATH_MAX)) == -1)