diff --git a/sphinx_d2lang/d2lang.py b/sphinx_d2lang/d2lang.py
index 2819bd1..ccdfe2e 100644
--- a/sphinx_d2lang/d2lang.py
+++ b/sphinx_d2lang/d2lang.py
@@ -25,7 +25,7 @@ class D2langDirective(SphinxDirective):
         if 'filename' in self.options:
             output_fname = self.options.get('filename')
         else:
-            output_fname = "d2lang_svg/" + str(uuid.uuid4())
+            output_fname = "d2lang_svg/" + str(uuid.uuid4()) + ".svg"
         if 'layout' in self.options:
             layout = self.options.get('layout')
         else: