diff --git a/docs/Project.toml b/docs/Project.toml
index f725f467a..cf9c4ecaf 100644
--- a/docs/Project.toml
+++ b/docs/Project.toml
@@ -15,6 +15,7 @@ Accessors = "0.1"
 DataStructures = "0.18"
 Distributions = "0.25"
 Documenter = "1"
+DocumenterMermaid = "0.1"
 FillArrays = "0.13, 1"
 ForwardDiff = "0.10"
 LogDensityProblems = "2"