diff --git a/requirements.txt b/requirements.txt
index 708abe6..cc7bf0e 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -126,6 +126,8 @@ sphinxcontrib-jsmath==1.0.1
     # via sphinx
 sphinxcontrib-qthelp==2.0.0
     # via sphinx
+sphinxcontrib-mermaid
+    # via sphinx
 sphinxcontrib-serializinghtml==2.0.0
     # via sphinx
 sphinxcontrib-video==0.4.1