diff --git a/sphinx_d2lang/d2lang.py b/sphinx_d2lang/d2lang.py
index ccdfe2e..4cb7df1 100644
--- a/sphinx_d2lang/d2lang.py
+++ b/sphinx_d2lang/d2lang.py
@@ -31,7 +31,7 @@ class D2langDirective(SphinxDirective):
         else:
             layout = 'dagre'
         if self.arguments:
-            path = Path(srcdir + self.arguments[0])
+            path = Path(srcdir + '/' + self.arguments[0])
             if path.is_file():
                 build_svg(self.arguments[0], srcdir, output_fname, layout)
             else: