diff --git a/blueprintcompiler/parser.py b/blueprintcompiler/parser.py
index 89e1533..1f87647 100644
--- a/blueprintcompiler/parser.py
+++ b/blueprintcompiler/parser.py
@@ -33,7 +33,9 @@ def parse(
         original_text = tokens[0].string if len(tokens) else ""
         ctx = ParseContext(tokens, original_text)
         AnyOf(UI).parse(ctx)
-        ast_node = ctx.last_group.to_ast() if ctx.last_group else None
+
+        assert ctx.last_group is not None
+        ast_node = ctx.last_group.to_ast()
 
         errors = [*ctx.errors, *ast_node.errors]
         warnings = [*ctx.warnings, *ast_node.warnings]
diff --git a/build-aux/install_deps.sh b/build-aux/install_deps.sh
index 381a57a..342778d 100755
--- a/build-aux/install_deps.sh
+++ b/build-aux/install_deps.sh
@@ -7,8 +7,8 @@ git clone --depth=1 https://gitlab.gnome.org/GNOME/gtk.git
 cd gtk
 meson setup builddir \
   --prefix=/usr \
-  -Dgtk_doc=true \
-  -Ddemos=false \
+  -Ddocumentation=true \
+  -Dbuild-demos=false \
   -Dbuild-examples=false \
   -Dbuild-tests=false \
   -Dbuild-testsuite=false