diff --git a/LICENSE b/LICENSE
index b20a237..6249e74 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,19 +1,19 @@
-Copyright © 2004-2017 by René Nyffenegger
+zlib License
 
-This source code is provided 'as-is', without any express or implied
-warranty. In no event will the author be held liable for any damages
+Copyright (c) 2004-2017 René Nyffenegger
+
+This software is provided 'as-is', without any express or implied
+warranty.  In no event will the authors be held liable for any damages
 arising from the use of this software.
-                                                                              
+
 Permission is granted to anyone to use this software for any purpose,
 including commercial applications, and to alter it and redistribute it
 freely, subject to the following restrictions:
-                                                                              
-1. The origin of this source code must not be misrepresented; you must not
-   claim that you wrote the original source code. If you use this source code
+
+1. The origin of this software must not be misrepresented; you must not
+   claim that you wrote the original software. If you use this software
    in a product, an acknowledgment in the product documentation would be
    appreciated but is not required.
-                                                                              
 2. Altered source versions must be plainly marked as such, and must not be
-   misrepresented as being the original source code.
-                                                                              
+   misrepresented as being the original software.
 3. This notice may not be removed or altered from any source distribution.
diff --git a/Makefile b/Makefile
index de8d7f6..851f747 100644
--- a/Makefile
+++ b/Makefile
@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: Zlib
+
 WARNINGS=                    \
    -Werror                   \
    -Wall                     \
diff --git a/base64.cpp b/base64.cpp
index 843719e..9bcb7d1 100644
--- a/base64.cpp
+++ b/base64.cpp
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Zlib
+
 /*
    base64.cpp and base64.h
 
diff --git a/base64.h b/base64.h
index 4860d63..6218606 100644
--- a/base64.h
+++ b/base64.h
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Zlib
+
 //
 //  base64 encoding and decoding with C++.
 //  Version: 2.rc.09 (release candidate)
diff --git a/measure-time.cpp b/measure-time.cpp
index 91d4df9..b560654 100644
--- a/measure-time.cpp
+++ b/measure-time.cpp
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Zlib
+
 #include "base64.h"
 #include <iostream>
 #include <chrono>
diff --git a/test-google.cpp b/test-google.cpp
index bc5090e..48e53fd 100644
--- a/test-google.cpp
+++ b/test-google.cpp
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Zlib
+
 #include "base64.h"
 #include <iostream>
 
diff --git a/test.cpp b/test.cpp
index 7cdbada..bae06bf 100644
--- a/test.cpp
+++ b/test.cpp
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Zlib
+
 #include "base64.h"
 #include <iostream>