diff --git a/07-Considering_Threadability.md b/07-Considering_Threadability.md
index 36c5cc7..c0d3a7e 100644
--- a/07-Considering_Threadability.md
+++ b/07-Considering_Threadability.md
@@ -8,4 +8,11 @@ Global data leads to unintended side effects between functions and can make code
 
 ## Avoid Heap Operations
 
-Much slower in threaded environments. In many or maybe even most cases, copying data is faster. Plus with move operations and such and things
+Much slower in threaded environments. In many or maybe even most cases, copying data is faster. Plus with move operations and such and things.
+
+## Mutex and mutable go together (M&M rule, C++11)
+For member variables it is good practice to use mutex and mutable together. This applies in both ways:
+* A mutable member variable is presumed to be a shared variable so it should be synchronized with a mutex (or made atomic)
+* If a member variable is itself a mutex, it should be mutable. This is required to use it inside a const member function.
+
+For more information see the following article from Herb Sutter: http://herbsutter.com/2013/05/24/gotw-6a-const-correctness-part-1-3/
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