diff --git a/configure.ac b/configure.ac
index 22e27f6f..82f6fccd 100644
--- a/configure.ac
+++ b/configure.ac
@@ -72,7 +72,8 @@ AC_CHECK_TYPES([mode_t, off_t, pid_t, size_t, ssize_t], , [AC_MSG_FAILURE([canno
 AC_FUNC_FORK
 AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK
 AC_FUNC_STRNLEN
-AC_CHECK_FUNCS([atexit dup2 ftruncate getcwd gettimeofday localtime_r memchr memset mkdir rmdir setlocale socket strcasecmp strchr strdup strerror strncasecmp strndup strrchr strspn strstr strtol strtoul], , [AC_MSG_FAILURE([cannot find the $ac_func function, which i3 requires])])
+AC_CHECK_FUNCS([atexit dup2 ftruncate getcwd gettimeofday localtime_r memchr memset mkdir rmdir setlocale socket strcasecmp strchr strdup strerror strncasecmp strrchr strspn strstr strtol strtoul], , [AC_MSG_FAILURE([cannot find the $ac_func function, which i3 requires])])
+AC_REPLACE_FUNCS([mkdirp strndup])
 
 # Checks for libraries.
 
diff --git a/include/libi3.h b/include/libi3.h
index 790baba9..15d1bc76 100644
--- a/include/libi3.h
+++ b/include/libi3.h
@@ -341,8 +341,7 @@ gchar *g_utf8_make_valid(const gchar *str, gssize len);
  */
 uint32_t get_colorpixel(const char *hex) __attribute__((const));
 
-#if defined(__APPLE__)
-
+#ifndef HAVE_strndup
 /**
  * Taken from FreeBSD
  * Returns a pointer to a new string which is a duplicate of the
@@ -350,7 +349,6 @@ uint32_t get_colorpixel(const char *hex) __attribute__((const));
  *
  */
 char *strndup(const char *str, size_t n);
-
 #endif
 
 /**
@@ -528,7 +526,7 @@ char *resolve_tilde(const char *path);
  */
 char *get_config_path(const char *override_configpath, bool use_system_paths);
 
-#if !defined(__sun)
+#ifndef HAVE_mkdirp
 /**
  * Emulates mkdir -p (creates any missing folders)
  *
diff --git a/libi3/mkdirp.c b/libi3/mkdirp.c
index f5281bd7..35a30475 100644
--- a/libi3/mkdirp.c
+++ b/libi3/mkdirp.c
@@ -12,12 +12,11 @@
 #include <string.h>
 #include <sys/stat.h>
 
+#ifndef HAVE_mkdirp
 /*
  * Emulates mkdir -p (creates any missing folders)
  *
  */
-
-#if !defined(__sun)
 int mkdirp(const char *path, mode_t mode) {
     if (mkdir(path, mode) == 0)
         return 0;
diff --git a/libi3/strndup.c b/libi3/strndup.c
index e17f843c..e215a76f 100644
--- a/libi3/strndup.c
+++ b/libi3/strndup.c
@@ -10,8 +10,7 @@
 #include <sys/types.h>
 #include <string.h>
 
-#if defined(__APPLE__)
-
+#ifndef HAVE_strndup
 /*
  * Taken from FreeBSD
  * Returns a pointer to a new string which is a duplicate of the
@@ -30,5 +29,4 @@ char *strndup(const char *str, size_t n) {
     copy[len] = '\0';
     return (copy);
 }
-
 #endif