diff --git a/ChangeLog b/ChangeLog
index 20831bf20b..9578518057 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+Fri Dec 28 23:12:44 2012  Charlie Somerville  <charlie@charliesomerville.com>
+
+	* configure.in: check for the whether crt_externs.h is present when compiling
+	  for darwin (this header is missing in the iOS SDK)
+	* eval_intern.h: check HAVE_CRT_EXTERNS_H before including crt_externs.h, if
+	  not defined, include missing/crt_externs.h instead
+	* hash.c: ditto
+	* missing/setproctitle.c: ditto
+	* missing/crt_externs.h: declare _NSGetEnviron() function and define environ
+	  for iOS
+
 Fri Dec 28 21:40:36 2012  Keiju Ishitsuka  <keiju@ishitsuka.com>
 
 	* lib/irb/context.rb: IRB::Context#new: Check from JobManager
diff --git a/configure.in b/configure.in
index 3648814a9f..9e97d6113d 100644
--- a/configure.in
+++ b/configure.in
@@ -1220,6 +1220,12 @@ main()
 		    LINK_SO="$LINK_SO
 $POSTLINK"
 		fi
+		AC_CACHE_CHECK(whether crt_externs.h is present for extern macro, rb_cv_crt_externs,
+		    [AC_TRY_COMPILE([ #include <crt_externs.h> ], [return 0;],
+		    rb_cv_crt_externs=yes, rb_cv_crt_externs=no)])
+		if test "$rb_cv_crt_externs" = yes; then
+		    AC_DEFINE(HAVE_CRT_EXTERNS_H)
+		fi
 		],
 [hpux*], [	LIBS="-lm $LIBS"
 		ac_cv_c_inline=no],
diff --git a/eval_intern.h b/eval_intern.h
index ed27b8ba85..334b8d439a 100644
--- a/eval_intern.h
+++ b/eval_intern.h
@@ -28,7 +28,11 @@
 #include <setjmp.h>
 
 #ifdef __APPLE__
-#include <crt_externs.h>
+# ifdef HAVE_CRT_EXTERNS_H
+#  include <crt_externs.h>
+# else
+#  include "missing/crt_externs.h"
+# endif
 #endif
 
 #ifndef HAVE_STRING_H
diff --git a/hash.c b/hash.c
index 68955b241c..cba71f948f 100644
--- a/hash.c
+++ b/hash.c
@@ -20,7 +20,11 @@
 #include "probes.h"
 
 #ifdef __APPLE__
-#include <crt_externs.h>
+# ifdef HAVE_CRT_EXTERNS_H
+#  include <crt_externs.h>
+# else
+#  include "missing/crt_externs.h"
+# endif
 #endif
 
 static VALUE rb_hash_s_try_convert(VALUE, VALUE);
diff --git a/missing/crt_externs.h b/missing/crt_externs.h
new file mode 100644
index 0000000000..cc96d46738
--- /dev/null
+++ b/missing/crt_externs.h
@@ -0,0 +1,8 @@
+#ifndef MISSING_CRT_EXTERNS_H
+#define MISSING_CRT_EXTERNS_H
+
+char ***_NSGetEnviron();
+#undef environ
+#define environ (*_NSGetEnviron())
+
+#endif
diff --git a/missing/setproctitle.c b/missing/setproctitle.c
index d35e70d534..9dcf37560b 100644
--- a/missing/setproctitle.c
+++ b/missing/setproctitle.c
@@ -49,9 +49,13 @@
 #include <string.h>
 
 #if defined(__APPLE__)
-#include <crt_externs.h>
-#undef environ
-#define environ (*_NSGetEnviron())
+# ifdef HAVE_CRT_EXTERNS_H
+#  include <crt_externs.h>
+#  undef environ
+#  define environ (*_NSGetEnviron())
+# else
+#  include "crt_externs.h"
+# endif
 #endif
 
 #define SPT_NONE	0	/* don't use it at all */