diff --git a/marimo/_output/formatters/iframe.py b/marimo/_output/formatters/iframe.py
index 7145cac65a7..b24f19603f8 100644
--- a/marimo/_output/formatters/iframe.py
+++ b/marimo/_output/formatters/iframe.py
@@ -1,8 +1,15 @@
 # Copyright 2025 Marimo. All rights reserved.
 from __future__ import annotations
 
+import re
 from html.parser import HTMLParser
 
+_SCRIPT_INLINE_RE = re.compile(
+    # matches <script ...> that does NOT have 'src=' before the close '>'
+    r"<script\b(?![^>]*\bsrc\s*=)",
+    re.IGNORECASE,
+)
+
 
 def maybe_wrap_in_iframe(html_content: str) -> str:
     if _has_script_tag_without_src(html_content):
@@ -17,6 +24,10 @@ def _has_script_tag_without_src(html_content: str) -> bool:
     if "<script" not in html_content:
         return False
 
+    # Fast regex check for <script ...> without src
+    if not _SCRIPT_INLINE_RE.search(html_content):
+        return False
+
     parser = ScriptTagParser()
     try:
         parser.feed(html_content)  # type: ignore
diff --git a/marimo/_output/formatting.py b/marimo/_output/formatting.py
index 447bd915ca7..8ca760c8f57 100644
--- a/marimo/_output/formatting.py
+++ b/marimo/_output/formatting.py
@@ -148,9 +148,8 @@ def get_formatter(
         get_context()
     except ContextNotInitializedError:
         if FORMATTERS.is_empty():
-            from marimo._output.formatters.formatters import (
-                register_formatters,
-            )
+            from marimo._output.formatters.formatters import \
+                register_formatters
 
             # Install formatters when marimo is being used without
             # a kernel (eg, in a unit test or when run as a Python script)