diff --git a/configure.ac b/configure.ac
index 85d65ff..d8a8ee2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -47,6 +47,9 @@ case "${target_os}" in
     ELK_LDFLAGS="${ELK_LDFLAGS} -no-undefined"
     MATH_LIBS=""
     ;;
+  *darwin*)
+    AC_DEFINE(SYS_DARWIN, 1, Define if the system is Darwin)],
+    ;;
 esac
 ELK_LIBS="${ELK_LIBS} ${MATH_LIBS}"
 
diff --git a/lib/unix/process.c b/lib/unix/process.c
index 8e9d85c..2af9497 100644
--- a/lib/unix/process.c
+++ b/lib/unix/process.c
@@ -39,13 +39,13 @@
 
 #ifndef WIN32
 
-#ifdef ENVIRON_IN_UNISTD_H
+#ifndef ENVIRON_IN_UNISTD_H
 /* "extern" in front of the next declaration causes the Ultrix 4.2 linker
  * to fail, but omitting it no longer works with modern C compilers: */
 extern char **environ;
 #endif
 
-#ifdef HAVE_ENVIRON
+#if defined(HAVE_ENVIRON) && !defined(SYS_DARWIN)
 static Object P_Environ() {
     Object ret, cell, str;
     char *p, **ep;