diff --git a/README.md b/README.md
index 54496fa..6adca38 100644
--- a/README.md
+++ b/README.md
@@ -9,6 +9,10 @@ Requirements
 
  * PHP >= 5.3
 
+Suggested PHP extensions
+ 
+ * mbstring - Used for calculating string widths.
+
 Function List
 -------------