diff --git a/Makefile b/Makefile
index f199f29..25e44f4 100644
--- a/Makefile
+++ b/Makefile
@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: Apache-2.0
 CC=gcc
 CFLAGS= -g3 -O0 -Wall -Wextra
 INCLUDE_DIR=/usr/local/include/
diff --git a/bit.c b/bit.c
index 6d3509f..315df80 100644
--- a/bit.c
+++ b/bit.c
@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+
 /* INCLUDES ==================================================================*/
 
 /* 
diff --git a/bit.h b/bit.h
index 0826bb2..b514aea 100644
--- a/bit.h
+++ b/bit.h
@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: Apache-2.0 */
+
 #ifndef _BIT_H
 #define _BIT_H
 
diff --git a/testbench.c b/testbench.c
index badfa75..7f5d211 100644
--- a/testbench.c
+++ b/testbench.c
@@ -1,4 +1,4 @@
-
+/* SPDX-License-Identifier: Apache-2.0 */
 /* INCLUDES ==================================================================*/
 
 #include <stdio.h>