diff --git a/spec.md b/spec.md
index 201cc89..2d75291 100644
--- a/spec.md
+++ b/spec.md
@@ -312,8 +312,8 @@ clear reasons for doing otherwise.
 We define the function $\operatorname{CP32} \in V_8 \rightarrow U_{32}$
 as:
 
-$\operatorname{CP32}(X) = \bigoplus_{i = 0}^{|X| - 1}
-\operatorname{ROT}_L(g(X_i), |X| - i + 1)$
+- $\operatorname{CP32}(X) = \bigoplus_{i = 0}^{|X| - 1} \operatorname{ROT}_L(g(X_i), |X| - i - 1)$ if $|X| > 0$
+- 0 otherwise
 
 Where $g(n) = G_n$ and the sequence $G \in V_{32}$ is defined in the
 appendix.