diff --git a/ocaml-dune.spec b/ocaml-dune.spec
index 8709a07..afb6b9a 100644
--- a/ocaml-dune.spec
+++ b/ocaml-dune.spec
@@ -17,6 +17,7 @@ BuildRequires:  ocaml-findlib-devel
 
 # Depend on /usr/bin/sphinx-build for python version invariance.
 BuildRequires:  /usr/bin/sphinx-build
+BuildRequires:  python3-sphinx_rtd_theme
 
 # Required by tests.
 BuildRequires:  git
@@ -107,6 +108,7 @@ cp -ar README.md CHANGES.md doc/_build/* %{buildroot}%{_pkgdocdir}/
 %changelog
 * Wed Mar 13 2019 Andy Li <andy@onthewings.net> - 1.8.2-1
 - Updated to latest upstream release (#1686836).
+- Add missing dependency on sphinx_rtd_theme.
 
 * Fri Mar 08 2019 Andy Li <andy@onthewings.net> - 1.8.0-1
 - Updated to latest upstream release (#1686466).