diff --git a/configure.ac b/configure.ac
index d22bba15e2..d656ccf898 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3594,6 +3594,7 @@ AS_IF([test "${ARCH_FLAG}"], [
     CXXFLAGS=`echo "$CXXFLAGS" | sed "s| *$archflagpat"'||'`
     LDFLAGS=`echo "$LDFLAGS" | sed "s| *$archflagpat"'||'`
 ])
+rb_cv_warnflags=`echo "$rb_cv_warnflags" | sed 's/^ */;s/ *$/'`
 warnflags="$rb_cv_warnflags"
 AC_SUBST(cppflags)dnl
 AC_SUBST(cflags, ["${orig_cflags:+$orig_cflags }"'${optflags} ${debugflags} ${warnflags}'])dnl