diff --git a/exercises/020-factorial/README.md b/exercises/020-factorial/README.md
index a835ba34..44db1662 100644
--- a/exercises/020-factorial/README.md
+++ b/exercises/020-factorial/README.md
@@ -19,3 +19,4 @@ factorial(8)
 ## 💡 Hint:
 
 + If you don't know what a factorial is, you can check it out on this link: https://www.cuemath.com/numbers/factorial/
++ Every recursive function must have a base case to prevent infinite recursion.