diff --git a/Makefile b/Makefile
index a8252d4..4532a15 100644
--- a/Makefile
+++ b/Makefile
@@ -13,7 +13,7 @@ develop: venv ## Install the dev dependencies
 	venv/bin/pip install -e ".[dev,docs]"
 docs: cog ## Build the docs
 	venv/bin/sphinx-build docs public
-	if [[ ! -e public/mermaid.min.js ]]; then curl -sL $$(grep mermaid.min.js public/search.html | cut -f 2 -d '"') --output public/mermaid.min.js; fi
+	if [ ! -e "public/mermaid.min.js" ]; then curl -sL $$(grep mermaid.min.js public/search.html | cut -f 2 -d '"') --output public/mermaid.min.js; fi
 	sed -e 's@https://unpkg.com/mermaid[^"]*"@mermaid.min.js"@' -i public/search.html public/genindex.html
 	sed -e 's@https://unpkg.com/mermaid[^"]*"@../mermaid.min.js"@' -i public/developer/models.html public/developer/overview.html
 cog: ## Run cog, to integrate the CLI options to the docs.