diff --git a/ChangeLog b/ChangeLog
index 910a248bb8..7344e03f29 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Jul 24 00:16:13 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* configure.in: changed default optflags to -O0 if the compiler is
+	  llvm-gcc. It prevent ruby crash on OS X 10.7 (Lion).
+
 Sun Jul 24 00:05:00 2011  Jeremy Evans  <merch-redmine@jeremyevans.net>
 
 	* error.c (rb_name_error_str): new function to raise NameError
diff --git a/configure.in b/configure.in
index 29c5c126eb..b90f689e8b 100644
--- a/configure.in
+++ b/configure.in
@@ -277,7 +277,13 @@ AC_PROG_GCC_TRADITIONAL
 AC_SUBST(GCC)
 if test "$GCC" = yes; then
     linker_flag=-Wl,
-    : ${optflags=-O3}
+    if test "$CC -v 2>&1 | grep LLVM" ; then
+	# llvm-gcc's optimization strategy is far different from gcc.
+	# It makes confusing our gcc specific optimized code.
+	: ${optflags=-O0}
+    else
+	: ${optflags=-O3}
+    fi
     AS_CASE(["$target_os"], [linux*|darwin*], [: ${debugflags=-ggdb}])
     RUBY_APPEND_OPTIONS(XCFLAGS, ["-include ruby/config.h" "-include ruby/missing.h"])
 else