diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index a5a5111f..031f51f5 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -135,9 +135,9 @@ balance the lines.
 
 ### Line Length
 
-Try to keep your lines under 80 columns, but you can go up to 100 if it
-improves readability. Don't break lines indiscriminately, try to find nice
-breaking points so your code is easy to read.
+Try to keep your lines under 80 columns, assuming a tab width equal to 4 spaces,
+but you can go up to 100 if it improves readability. Don't break lines
+indiscriminately, try to find nice breaking points so your code is easy to read.
 
 ### Names