diff --git a/API.md b/API.md
index d2efadf..b0c676a 100644
--- a/API.md
+++ b/API.md
@@ -17,12 +17,13 @@ are true at all times for all players:
 
 * Current and maximum mana can never be smaller than 0
 * The current value must not be greater than the maximum value
+* Only integer numbers are permitted for mana values
 
 It should be not possible to break these rules using this API alone.
 If you somehow manage to break one ofthe rules, please report a bug.
 
-Furthermore, real numbers may be used as values, but it is not
-recommended.
+If a real number is used as input for a value, it will be rounded
+(“round up half” rule).
 
 ## Functions
 Of not specified otherwise, all functions return `nil`.