diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 08f5586c55a..cea5622e1bd 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,5 +1,8 @@
 2015-05-26  Jason Merrill  <jason@redhat.com>
 
+	* configure.ac: Set CXXFLAGS for ISL test.
+	* configure: Regenerate.
+
 	* configure.ac: Use C++ for all tests.  Use AC_CHECK_DECLS for
 	strstr and basename.
 	* configure: Regenerate.
diff --git a/gcc/configure b/gcc/configure
index 6d808be3c96..a62f232f55d 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -28286,8 +28286,8 @@ fi
 # Check whether isl_schedule_constraints_compute_schedule is available;
 # it's new in ISL-0.13.
 if test "x${ISLLIBS}" != "x" ; then
-  saved_CFLAGS="$CFLAGS"
-  CFLAGS="$CFLAGS $ISLINC"
+  saved_CXXFLAGS="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS $ISLINC"
   saved_LIBS="$LIBS"
   LIBS="$LIBS $ISLLIBS $GMPLIBS"
 
@@ -28315,7 +28315,7 @@ rm -f core conftest.err conftest.$ac_objext \
 $as_echo "$ac_has_isl_schedule_constraints_compute_schedule" >&6; }
 
   LIBS="$saved_LIBS"
-  CFLAGS="$saved_CFLAGS"
+  CXXFLAGS="$saved_CXXFLAGS"
 
   if test x"$ac_has_isl_schedule_constraints_compute_schedule" = x"yes"; then
 
diff --git a/gcc/configure.ac b/gcc/configure.ac
index 5f9ed924fdb..71b5f4f4c7f 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -5712,8 +5712,8 @@ fi
 # Check whether isl_schedule_constraints_compute_schedule is available;
 # it's new in ISL-0.13.
 if test "x${ISLLIBS}" != "x" ; then
-  saved_CFLAGS="$CFLAGS"
-  CFLAGS="$CFLAGS $ISLINC"
+  saved_CXXFLAGS="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS $ISLINC"
   saved_LIBS="$LIBS"
   LIBS="$LIBS $ISLLIBS $GMPLIBS"
 
@@ -5725,7 +5725,7 @@ if test "x${ISLLIBS}" != "x" ; then
   AC_MSG_RESULT($ac_has_isl_schedule_constraints_compute_schedule)
 
   LIBS="$saved_LIBS"
-  CFLAGS="$saved_CFLAGS"
+  CXXFLAGS="$saved_CXXFLAGS"
 
   if test x"$ac_has_isl_schedule_constraints_compute_schedule" = x"yes"; then
      AC_DEFINE(HAVE_ISL_SCHED_CONSTRAINTS_COMPUTE_SCHEDULE, 1,