diff --git a/sphinx_d2lang/d2lang.py b/sphinx_d2lang/d2lang.py
index f2c11b7..78f1dae 100644
--- a/sphinx_d2lang/d2lang.py
+++ b/sphinx_d2lang/d2lang.py
@@ -16,8 +16,9 @@ class D2langDirective(Directive):
         srcdir = self.state.document.settings.env.srcdir
         diag_source = self.content
         with tempfile.NamedTemporaryFile() as fp:
-            for line in self.content:
+            for line in self.content.splitlines():
                 fp.write(bytes(line,'utf-8'))
+            fp.seek(0)
             cmd_line = '%s %s %s' % (d2_bin, fp.name, srcdir + "/test.svg")
             args = shlex.split(cmd_line)
             subprocess.run(args)