diff --git a/book/figures/vars.tex b/book/figures/vars.tex
index d87e959..e9555ff 100644
--- a/book/figures/vars.tex
+++ b/book/figures/vars.tex
@@ -1,6 +1,7 @@
 \documentclass[tikz]{standalone}
 \usepackage{tikz}
 \usepackage{pgfplots}
+\usepackage{chemfig}
 \usepackage[mode=match, reset-text-family=false]{siunitx}
 \DeclareSIUnit\degF{\text{°}F}
 \input{flowcharts_tikz.tex}