diff --git a/test/test_main.cpp b/test/test_main.cpp
index 5ea5ccf..f9d9f72 100644
--- a/test/test_main.cpp
+++ b/test/test_main.cpp
@@ -15,6 +15,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //
+// SPDX-License-Identifier: Apache-2.0
+//
 
 #define CATCH_CONFIG_MAIN
 #include "catch.hpp"
diff --git a/test/test_wint.cpp b/test/test_wint.cpp
index b12b405..2bbfeb0 100644
--- a/test/test_wint.cpp
+++ b/test/test_wint.cpp
@@ -15,6 +15,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //
+// SPDX-License-Identifier: Apache-2.0
+//
 
 #include "wideint.hpp"
 
diff --git a/test/test_wuint.cpp b/test/test_wuint.cpp
index 770dac6..c235133 100644
--- a/test/test_wuint.cpp
+++ b/test/test_wuint.cpp
@@ -15,6 +15,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //
+// SPDX-License-Identifier: Apache-2.0
+//
 
 #include "wideint.hpp"
 
diff --git a/wideint.hpp b/wideint.hpp
index 9601a7d..83842bc 100644
--- a/wideint.hpp
+++ b/wideint.hpp
@@ -15,6 +15,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //
+// SPDX-License-Identifier: Apache-2.0
+//
 
 #pragma once