diff --git a/src/core/ccitt.js b/src/core/ccitt.js
index 827bc0754..a18b4fcf7 100644
--- a/src/core/ccitt.js
+++ b/src/core/ccitt.js
@@ -12,6 +12,12 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+/* Copyright 1996-2003 Glyph & Cog, LLC
+ *
+ * The CCIT stream implementation contained in this file is a JavaScript port
+ * of XPDF's implementation, made available under the Apache 2.0 open source
+ * license.
+ */
 
 /**
  * @typedef {Object} CCITTFaxDecoderSource
diff --git a/src/core/stream.js b/src/core/stream.js
index fa89207dc..ae57f9023 100644
--- a/src/core/stream.js
+++ b/src/core/stream.js
@@ -12,6 +12,12 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+/* Copyright 1996-2003 Glyph & Cog, LLC
+ *
+ * The flate stream implementation contained in this file is a JavaScript port
+ * of XPDF's implementation, made available under the Apache 2.0 open source
+ * license.
+ */
 
 import { FormatError, isSpace, stringToBytes } from '../shared/util';
 import { isDict } from './primitives';