diff --git a/ch04_keys.adoc b/ch04_keys.adoc
index fdd41a7b..cc5f138b 100644
--- a/ch04_keys.adoc
+++ b/ch04_keys.adoc
@@ -779,7 +779,7 @@ As we saw in the section <<public_key_derivation>>, a public key is a point (x,
 elliptic curve. Because the curve expresses a mathematical function, a
 point on the curve represents a solution to the equation and, therefore,
 if we know the _x_ coordinate, we can calculate the _y_ coordinate by
-solving the equation y^2^ mod p = (x^3^ + 7) mod p. That allows us to
+solving the equation [.keep-together]#y^2^ mod p = (x^3^ + 7) mod p.# That allows us to
 store only the _x_ coordinate of the public key point, omitting the _y_
 coordinate and reducing the size of the key and the space required to
 store it by 256 bits. An almost 50% reduction in size in every