diff --git a/src/PIL/DdsImagePlugin.py b/src/PIL/DdsImagePlugin.py
index 9508e61c8..e755f94b9 100644
--- a/src/PIL/DdsImagePlugin.py
+++ b/src/PIL/DdsImagePlugin.py
@@ -3,7 +3,7 @@ A Pillow loader for .dds files (S3TC-compressed aka DXTC)
 Jerome Leclanche <jerome@leclan.ch>
 
 Documentation:
-  http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt
+  https://web.archive.org/web/20170802060935/http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt
 
 The contents of this file are hereby released in the public domain (CC0)
 Full text of the CC0 license:
diff --git a/src/PIL/PdfParser.py b/src/PIL/PdfParser.py
index ceea7dd2e..c18846068 100644
--- a/src/PIL/PdfParser.py
+++ b/src/PIL/PdfParser.py
@@ -341,7 +341,7 @@ def pdf_repr(x):
 
 
 class PdfParser:
-    """Based on http://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/PDF32000_2008.pdf
+    """Based on https://www.adobe.com/content/dam/acom/en/devnet/acrobat/pdfs/PDF32000_2008.pdf
     Supports PDF up to 1.4
     """
 
diff --git a/src/libImaging/BcnDecode.c b/src/libImaging/BcnDecode.c
index 58d3ecc10..1472b0296 100644
--- a/src/libImaging/BcnDecode.c
+++ b/src/libImaging/BcnDecode.c
@@ -4,7 +4,7 @@
  * decoder for DXTn-compressed data
  *
  * Format documentation:
- *   http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt
+ *   https://web.archive.org/web/20170802060935/http://oss.sgi.com/projects/ogl-sample/registry/EXT/texture_compression_s3tc.txt
  *
  * The contents of this file are in the public domain (CC0)
  * Full text of the CC0 license:
@@ -178,7 +178,7 @@ static void decode_bc5_block(rgba *col, const UINT8* src) {
 }
 
 /* BC6 and BC7 are described here:
-   https://www.opengl.org/registry/specs/ARB/texture_compression_bptc.txt */
+   https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_texture_compression_bptc.txt */
 
 static UINT8 get_bit(const UINT8* src, int bit) {
 	int by = bit >> 3;