diff --git a/src/math.sol b/src/math.sol
index 5ea5761..034b116 100644
--- a/src/math.sol
+++ b/src/math.sol
@@ -13,6 +13,7 @@
 // You should have received a copy of the GNU General Public License
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+// SPDX-License-Identifier: GPL-3.0-or-later
 pragma solidity >0.4.13;
 
 contract DSMath {
diff --git a/src/math.t.sol b/src/math.t.sol
index c82b763..9a83152 100644
--- a/src/math.t.sol
+++ b/src/math.t.sol
@@ -11,6 +11,7 @@
 // You should have received a copy of the GNU General Public License
 // along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+// SPDX-License-Identifier: GPL-3.0-or-later
 pragma solidity >0.4.13;
 
 import "ds-test/test.sol";