diff --git a/ch01.asciidoc b/ch01.asciidoc
index 22540968..cfc8da67 100644
--- a/ch01.asciidoc
+++ b/ch01.asciidoc
@@ -509,7 +509,7 @@ include::code-ch01/answers.py[tag=exercise5,indent=0]
 [NOTE]
 ====
 The answer to Exercise 5 is why we choose to use finite fields with a _prime_ number of elements.
-No matter what _k_ you choose, as long as it's greater than 0, multiplying the entire set by _k_ will result in the same set as you started with.
+No matter what _k_ you choose, as long as it's greater than 0 (and different from the order of the set), multiplying the entire set by _k_ will result in the same set as you started with.
 
 Intuitively, the fact that we have a prime order results in every element of a finite field being equivalent.
 If the order of the set was a composite number, multiplying the set by one of the divisors would result in a smaller set.