diff --git a/README.md b/README.md
index 5b58ee6..39bdc67 100644
--- a/README.md
+++ b/README.md
@@ -732,8 +732,8 @@ Write code on a whiteboard or paper, not a computer. Test with some sample input
         - [ ] [Bit Manipulation](https://en.wikipedia.org/wiki/Bit_manipulation)
         - [ ] [Bitwise Operation](https://en.wikipedia.org/wiki/Bitwise_operation)
         - [ ] [Bithacks](https://graphics.stanford.edu/~seander/bithacks.html)
-        - [ ] [The Bit Twiddler](http://bits.stephan-brumme.com/)
-        - [ ] [The Bit Twiddler Interactive](http://bits.stephan-brumme.com/interactive.html)
+        - [ ] [The Bit Twiddler](https://bits.stephan-brumme.com/)
+        - [ ] [The Bit Twiddler Interactive](https://bits.stephan-brumme.com/interactive.html)
     - [ ] 2s and 1s complement
         - [Binary: Plusses & Minuses (Why We Use Two's Complement) (video)](https://www.youtube.com/watch?v=lKTsv6iVxV4)
         - [1s Complement](https://en.wikipedia.org/wiki/Ones%27_complement)
@@ -743,11 +743,11 @@ Write code on a whiteboard or paper, not a computer. Test with some sample input
         - [Count Bits](https://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetKernighan)
         - [How To Count The Number Of Set Bits In a 32 Bit Integer](http://stackoverflow.com/questions/109023/how-to-count-the-number-of-set-bits-in-a-32-bit-integer)
     - [ ] round to next power of 2:
-        - [Round Up To Next Power Of Two](http://bits.stephan-brumme.com/roundUpToNextPowerOfTwo.html)
+        - [Round Up To Next Power Of Two](https://bits.stephan-brumme.com/roundUpToNextPowerOfTwo.html)
     - [ ] swap values:
-        - [Swap](http://bits.stephan-brumme.com/swap.html)
+        - [Swap](https://bits.stephan-brumme.com/swap.html)
     - [ ] absolute value:
-        - [Absolute Integer](http://bits.stephan-brumme.com/absInteger.html)
+        - [Absolute Integer](https://bits.stephan-brumme.com/absInteger.html)
 
 </details>