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 887649441..1472b0296 100644
--- a/src/libImaging/BcnDecode.c
+++ b/src/libImaging/BcnDecode.c
@@ -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;