diff --git a/datetimes.Rmd b/datetimes.Rmd
index 910e120..a1a3e0b 100644
--- a/datetimes.Rmd
+++ b/datetimes.Rmd
@@ -481,7 +481,7 @@ To find out how many periods fall into an interval, you need to use integer divi
 
 How do you pick between duration, periods, and intervals? As always, pick the simplest data structure that solves your problem. If you only care about physical time, use a duration; if you need to add human times, use a period; if you need to figure out how long a span is in human units, use an interval.
 
-Figure \@{ref:dt-algebra} summarises permitted arithmetic operations between the different data types.
+Figure \@(ref:dt-algebra) summarises permitted arithmetic operations between the different data types.
 
 ```{r dt-algebra, echo = FALSE, fig.cap = "The allowed arithmetic operations between pairs of date/time classes."}
 knitr::include_graphics("diagrams/datetimes-arithmetic.png")