diff --git a/acinclude.m4 b/acinclude.m4
index a0eb13adc..ae78d9761 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -84,10 +84,10 @@ double d = 909042349670368103374704789055050114762116927356156320147971208440534
 
 ]])], [
 
-if grep noonsees conftest.$ac_objext >/dev/null ; then
+if grep -a noonsees conftest.$ac_objext >/dev/null ; then
   ax_cv_c_float_words_bigendian=yes
 fi
-if grep seesnoon conftest.$ac_objext >/dev/null ; then
+if grep -a seesnoon conftest.$ac_objext >/dev/null ; then
   if test "$ax_cv_c_float_words_bigendian" = unknown; then
     ax_cv_c_float_words_bigendian=no
   else