diff --git a/ch04.asciidoc b/ch04.asciidoc
index 2e22c5cf..a376471a 100644
--- a/ch04.asciidoc
+++ b/ch04.asciidoc
@@ -29,7 +29,7 @@ A private key is a number, between +1+ and +n - 1+ where latexmath:[\(n = 1.158
 	
 [TIP]
 ====
-Do not try and design your own pseudo random number generator (PRNG). Use a cryptographically-secure (CSPRNG) with a seed from a source of sufficient entropy, the choice of which which depends on you operating-system. Correct implementation of the CSPRNG is critical to the security of the keys. DIY is highly discouraged unless you are a professional cryptographer. 
+Do not try and design your own pseudo random number generator (PRNG). Use a cryptographically-secure pseudo-random number generator (CSPRNG) with a seed from a source of sufficient entropy, the choice of which depends on your operating-system. Correct implementation of the CSPRNG is critical to the security of the keys. DIY is highly discouraged unless you are a professional cryptographer. 
 ====