diff --git a/sphinx_d2lang/d2lang.py b/sphinx_d2lang/d2lang.py
index 48c5d5b..cb343aa 100644
--- a/sphinx_d2lang/d2lang.py
+++ b/sphinx_d2lang/d2lang.py
@@ -40,7 +40,7 @@ class D2langDirective(SphinxDirective):
         image_node = nodes.image(uri=output_fname)
         return [image_node]
 
-def build_svg(diag_src, out_dir, filename, layout)
+def build_svg(diag_src, out_dir, filename, layout):
     d2_bin = which('d2')
     cmd_line = '%s -l %s %s %s' % (d2_bin, layout, diag_src, out_dir + "/" + filename)
     args = shlex.split(cmd_line)