diff --git a/src/psc/app.py b/src/psc/app.py
index 55fd890..875cfd2 100644
--- a/src/psc/app.py
+++ b/src/psc/app.py
@@ -20,7 +20,6 @@
 from psc.resources import Resources
 from psc.resources import get_resources
 
-
 templates = Jinja2Templates(directory=HERE / "templates")
 
 
@@ -68,6 +67,14 @@ async def example(request: Request) -> _TemplateResponse:
     this_example = resources.examples[example_path]
     root_path = "../../.."
 
+    # Set the pyscript URL to the CDN if we are being built from
+    # the ``psc build`` command.
+    user_agent = request.headers["user-agent"]
+    if user_agent == "testclient":
+        pyscript_url = "https://pyscript.net/latest/pyscript.js"
+    else:
+        pyscript_url = f"{root_path}/pyscript/pyscript.js"
+
     return templates.TemplateResponse(
         "example.jinja2",
         dict(
@@ -77,6 +84,7 @@ async def example(request: Request) -> _TemplateResponse:
             body=this_example.body,
             request=request,
             root_path=root_path,
+            pyscript_url=pyscript_url,
         ),
     )
 
diff --git a/src/psc/resources.py b/src/psc/resources.py
index bf96c22..808b4bf 100644
--- a/src/psc/resources.py
+++ b/src/psc/resources.py
@@ -51,7 +51,8 @@ def get_head_nodes(s: BeautifulSoup) -> str:
 
 def is_local(test_path: Path = PYODIDE) -> bool:
     """Use a policy to decide local vs. CDN mode."""
-    return test_path.exists()
+    pyscript_file = test_path / "pyscript.js"
+    return pyscript_file.exists()
 
 
 def get_body_content(s: BeautifulSoup, test_path: Path = PYODIDE) -> str:
diff --git a/src/psc/templates/example.jinja2 b/src/psc/templates/example.jinja2
index 3939624..a766282 100644
--- a/src/psc/templates/example.jinja2
+++ b/src/psc/templates/example.jinja2
@@ -1,7 +1,7 @@
 {% extends "layout.jinja2" %}
 {% block extra_head %}
     <meta name="subtitle" content="{{ subtitle }}">
-    <script defer src="{{ root_path }}/pyscript/pyscript.js"></script>
+    <script defer src="{{ pyscript_url }}"></script>
     {{ extra_head | safe }}{% endblock %}
 {% block main %}
     <main id="main_container" class="container">