diff --git a/Makefile.PL b/Makefile.PL
index ee8d06a..ed12e4f 100644
--- a/Makefile.PL
+++ b/Makefile.PL
@@ -308,7 +308,7 @@ WriteMakefile(
 	# this change broke a test under some environment, and thus, may
 	# break other applications eventually. I'm not sure if this is
 	# worth the trouble.
-	OPTIMIZE => $Config{optimize} . (($^O eq 'solaris' and !$Config{gccversion}) ? "" : " -O2"),
+	OPTIMIZE => $Config{optimize} . (($^O eq 'solaris' and !$Config{gccversion}) ? "" : " -O2 -std=gnu99"),
 	OPTIONAL( '6.48',
 		MIN_PERL_VERSION => '5.006',
 	),