diff --git a/include/attestation/HmacKeyManager.h b/include/attestation/HmacKeyManager.h
index 571a361..d725be1 100644
--- a/include/attestation/HmacKeyManager.h
+++ b/include/attestation/HmacKeyManager.h
@@ -14,6 +14,9 @@
  * limitations under the License.
  */
 
+#ifndef ATTESTATION_HMACKEYMANAGER_H
+#define ATTESTATION_HMACKEYMANAGER_H
+
 #include <array>
 
 namespace android {
@@ -29,4 +32,6 @@
 private:
     const std::array<uint8_t, 128> mHmacKey;
 };
-} // namespace android
\ No newline at end of file
+} // namespace android
+
+#endif // ATTESTATION_HMACKEYMANAGER_H
\ No newline at end of file