diff --git a/cryptography/hazmat/primitives/src/constant_time.c b/cryptography/hazmat/primitives/src/constant_time.c
index aaed11a..d9d5cbf 100644
--- a/cryptography/hazmat/primitives/src/constant_time.c
+++ b/cryptography/hazmat/primitives/src/constant_time.c
@@ -1,3 +1,20 @@
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+// implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+
+#include "constant_time.h"
+
+
 uint8_t Cryptography_constant_time_bytes_eq(uint8_t *a, size_t len_a,
                                             uint8_t *b, size_t len_b) {
     size_t i = 0;
diff --git a/cryptography/hazmat/primitives/src/constant_time.h b/cryptography/hazmat/primitives/src/constant_time.h
index 2cc2580..f8d7450 100644
--- a/cryptography/hazmat/primitives/src/constant_time.h
+++ b/cryptography/hazmat/primitives/src/constant_time.h
@@ -1,2 +1,21 @@
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+// implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+
+#ifndef _PYCA_CRYPTOGRAPHY_CONSTANT_TIME_H
+#define _PYCA_CRYPTOGRAPHY_CONSTANT_TIME_H
+
 uint8_t Cryptography_constant_time_bytes_eq(uint8_t *, size_t, uint8_t *,
                                             size_t);
+
+#endif