diff --git a/autogen.sh b/autogen.sh
index 06a5facd1..058cec892 100755
--- a/autogen.sh
+++ b/autogen.sh
@@ -59,8 +59,15 @@ checkvers() {
     return 0
 }
 
+# We use GNU sed-isms, so if `gsed' exists, use that instead.
+sed=sed
+if command -v gsed >/dev/null
+then
+    sed=gsed
+fi
+
 # Check autoconf version
-AC_VERSION=`autoconf --version | sed '/^autoconf/ {s/^.* \([1-9][0-9.]*\)$/\1/; q}'`
+AC_VERSION=`autoconf --version | $sed '/^autoconf/ {s/^.* \([1-9][0-9.]*\)$/\1/; q}'`
 if checkvers "$AC_VERSION" $ac_need_maj $ac_need_min ; then
     echo Found valid autoconf version $AC_VERSION
 else
@@ -69,7 +76,7 @@ else
 fi
 
 # Check automake version
-AM_VERSION=`automake --version | sed '/^automake/ {s/^.* \([1-9][0-9.]*\)$/\1/; q}'`
+AM_VERSION=`automake --version | $sed '/^automake/ {s/^.* \([1-9][0-9.]*\)$/\1/; q}'`
 if checkvers "$AM_VERSION" $am_need_maj $am_need_min $am_need_rev ; then
     echo Found valid automake version $AM_VERSION
 else
@@ -83,7 +90,7 @@ fi
 # letter - note that the shell -lt and -gt comparisons will fail with
 # test: 6b: integer expression expected if the number to compare
 # contains a non-digit
-LT_VERSION=`libtool --version | sed '/GNU libtool/ {s/^.* \([1-9][0-9a-zA-Z.]*\)$/\1/; s/[a-zA-Z]//g; q}'`
+LT_VERSION=`libtool --version | $sed '/GNU libtool/ {s/^.* \([1-9][0-9a-zA-Z.]*\)$/\1/; s/[a-zA-Z]//g; q}'`
 if checkvers "$LT_VERSION" $lt_need_maj $lt_need_min $lt_need_rev ; then
     echo Found valid libtool version $LT_VERSION
 else
diff --git a/buildnum.py b/buildnum.py
index c2cede7b5..eff4b449e 100755
--- a/buildnum.py
+++ b/buildnum.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 # --- BEGIN COPYRIGHT BLOCK ---
 # Copyright (C) 2020 Red Hat, Inc.
 # All rights reserved.
diff --git a/ldap/servers/plugins/pwdstorage/crypt_pwd.c b/ldap/servers/plugins/pwdstorage/crypt_pwd.c
index 59b139719..73c76802b 100644
--- a/ldap/servers/plugins/pwdstorage/crypt_pwd.c
+++ b/ldap/servers/plugins/pwdstorage/crypt_pwd.c
@@ -16,17 +16,23 @@
  *
  */
 
-#include <stdio.h>
-#include <string.h>
-#include <sys/types.h>
-#include <sys/socket.h>
 #if defined(hpux) || defined(LINUX) || defined(__FreeBSD__)
-#ifndef __USE_XOPEN
-#define __USE_XOPEN /* linux */
-#endif              /* __USE_XOPEN */
+# ifndef __USE_XOPEN
+#  define __USE_XOPEN /* linux */
+# endif              /* __USE_XOPEN */
+# ifndef _BSD_SOURCE
+#  define _BSD_SOURCE
+# endif              /* !defined(_BSD_SOURCE) */
 #endif
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
 
-#include <crypt.h>
+#ifndef __FreeBSD__
+# include <crypt.h>
+#endif
 #include "pwdstorage.h"
 
 /* characters used in crypt encoding */
diff --git a/ldap/servers/slapd/daemon.c b/ldap/servers/slapd/daemon.c
index e5b416965..0aa17e0e6 100644
--- a/ldap/servers/slapd/daemon.c
+++ b/ldap/servers/slapd/daemon.c
@@ -232,8 +232,8 @@ disk_mon_get_mount_point(char *dir)
 char *
 disk_mon_get_mount_point(char *dir)
 {
-    struct statvfs sb;
-    if (statvfs(dir, &sb) != 0) {
+    struct statfs sb;
+    if (statfs(dir, &sb) != 0) {
         return NULL;
     }
 
diff --git a/ldap/servers/slapd/dse.c b/ldap/servers/slapd/dse.c
index 4f0f85f11..0e22d3cec 100644
--- a/ldap/servers/slapd/dse.c
+++ b/ldap/servers/slapd/dse.c
@@ -1008,7 +1008,13 @@ dse_write_file_nolock(struct dse *pdse)
                  * We have now written to the tmp location, and renamed it
                  * we need to open and fsync the dir to make the rename stick.
                  */
-                int fp_configdir = open(pdse->dse_configdir, O_PATH | O_DIRECTORY);
+                int fp_configdir =
+#ifdef O_PATH
+                    open(pdse->dse_configdir, O_PATH | O_DIRECTORY)
+#else
+                    open(pdse->dse_configdir, O_RDONLY | O_DIRECTORY)
+#endif
+                    ;
                 if (fp_configdir != -1) {
                     fsync(fp_configdir);
                     close(fp_configdir);
diff --git a/ldap/servers/slapd/getsocketpeer.c b/ldap/servers/slapd/getsocketpeer.c
index 9e4ff2e96..d08e52e95 100644
--- a/ldap/servers/slapd/getsocketpeer.c
+++ b/ldap/servers/slapd/getsocketpeer.c
@@ -24,6 +24,13 @@
  */
 #include <private/pprio.h>
 
+#if !(defined(SO_PEERCRED) || defined(HAVE_PEERUCRED) || defined(HAVE_GETPEEREID))
+# include <string.h>
+# include <sys/types.h>
+# include <sys/stat.h>
+# include <errno.h>
+#endif
+
 int
 slapd_get_socket_peer(PRFileDesc *nspr_fd, uid_t *uid, gid_t *gid)
 {
@@ -74,10 +81,6 @@ slapd_get_socket_peer(PRFileDesc *nspr_fd, uid_t *uid, gid_t *gid)
         ret = 0;
 
 #else /* hpux / Solaris9 / some BSDs - file descriptor cooperative auth */
-#include <string.h>
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <errno.h>
     struct msghdr msg = {0};
     struct iovec iov;
     char dummy[8];
diff --git a/ldap/servers/slapd/ssl.c b/ldap/servers/slapd/ssl.c
index ca8c3b4bc..2d7ba3e01 100644
--- a/ldap/servers/slapd/ssl.c
+++ b/ldap/servers/slapd/ssl.c
@@ -14,6 +14,7 @@
 /* SSL-related stuff for slapd */
 
 #include <stdio.h>
+#include <libgen.h>
 #include <sys/param.h>
 #include <ssl.h>
 #include <nss.h>
@@ -2401,7 +2402,6 @@ slapd_get_unlocked_key_for_cert(CERTCertificate *cert, void *pin_arg)
 /*
  * Functions to extract key and cert from the NSS cert db.
  */
-#include <libgen.h>
 #include <seccomon.h>
 #include <secmodt.h>
 #include <certt.h>
diff --git a/lib/libaccess/lasip.cpp b/lib/libaccess/lasip.cpp
index cdb88eec5..f3af15bec 100644
--- a/lib/libaccess/lasip.cpp
+++ b/lib/libaccess/lasip.cpp
@@ -332,7 +332,7 @@ LASIpBuild(NSErr_t *errp, char *attr_name, CmpOp_t comparator, char *attr_patter
                     return (retcode);
             }
 
-            if (LASIpAddPatternIPv6(errp, netmask, &ipv6, &context->treetop_ipv6) != (int)NULL) {
+            if (LASIpAddPatternIPv6(errp, netmask, &ipv6, &context->treetop_ipv6) != 0) {
                 return LAS_EVAL_INVALID;
             }
         }