diff --git a/pelican/settings.py b/pelican/settings.py
index 98b1357e..715b94c0 100644
--- a/pelican/settings.py
+++ b/pelican/settings.py
@@ -592,6 +592,17 @@ def configure_settings(settings: Settings) -> Settings:
         else:
             raise Exception("Could not find the theme {}".format(settings["THEME"]))
 
+    # Clear CSS_FILE if the file doesn't exist in the theme
+    css_file = settings.get("CSS_FILE")
+    if css_file:
+        theme = settings["THEME"]
+        static_paths = settings.get("THEME_STATIC_PATHS", ["static"])
+        if not any(
+            os.path.isfile(os.path.join(theme, sp, "css", css_file))
+            for sp in static_paths
+        ):
+            settings["CSS_FILE"] = ""
+
     # standardize strings to lowercase strings
     for key in ["DEFAULT_LANG"]:
         if key in settings:
diff --git a/pelican/tests/test_theme.py b/pelican/tests/test_theme.py
index 0070078a..9c81002d 100644
--- a/pelican/tests/test_theme.py
+++ b/pelican/tests/test_theme.py
@@ -133,6 +133,61 @@ class TestTemplateInheritance(LoggedTestCase):
         self.assertNotIn("Proudly powered by", content)
         self.assertIn("New footer", content)
 
+    def test_simple_theme_no_css_link(self):
+        """The simple theme has no static/css/ directory, so the CSS_FILE
+        link should not be rendered."""
+
+        settings = read_settings(
+            path=None,
+            override={
+                "THEME": "simple",
+                "PATH": CONTENT_DIR,
+                "OUTPUT_PATH": self.temp_output,
+                "CACHE_PATH": self.temp_cache,
+                "SITEURL": "http://example.com",
+            },
+        )
+
+        pelican = Pelican(settings=settings)
+        mute(True)(pelican.run)()
+
+        with open(os.path.join(self.temp_output, "test-md-file.html")) as f:
+            content = f.read()
+
+        self.assertNotIn("/theme/css/main.css", content)
+
+    def test_child_theme_with_css_file(self):
+        """A child theme that provides static/css/main.css should have the
+        CSS_FILE link rendered."""
+
+        # Add a CSS file to the child theme
+        css_dir = os.path.join(self.temp_theme, "static", "css")
+        os.makedirs(css_dir)
+        with open(os.path.join(css_dir, "main.css"), "w") as f:
+            f.write("body { margin: 0; }")
+
+        settings = read_settings(
+            path=None,
+            override={
+                "THEME": self.temp_theme,
+                "PATH": CONTENT_DIR,
+                "OUTPUT_PATH": self.temp_output,
+                "CACHE_PATH": self.temp_cache,
+                "SITEURL": "http://example.com",
+            },
+        )
+
+        pelican = Pelican(settings=settings)
+        mute(True)(pelican.run)()
+
+        with open(os.path.join(self.temp_output, "test-md-file.html")) as f:
+            content = f.read()
+
+        self.assertIn(
+            'href="http://example.com/theme/css/main.css"',
+            content,
+        )
+
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/pelican/themes/simple/templates/base.html b/pelican/themes/simple/templates/base.html
index eb58d810..5ad38cff 100644
--- a/pelican/themes/simple/templates/base.html
+++ b/pelican/themes/simple/templates/base.html
@@ -9,7 +9,9 @@
       {% if SITESUBTITLE %}
         <meta name="description" content="{{ SITESUBTITLE }}" />
       {% endif %}
-      <link rel="stylesheet" href="{{ SITEURL }}/{{ THEME_STATIC_DIR }}/css/{{ CSS_FILE }}" />
+      {% if CSS_FILE %}
+        <link rel="stylesheet" href="{{ SITEURL }}/{{ THEME_STATIC_DIR }}/css/{{ CSS_FILE }}" />
+      {% endif %}
       {% if STYLESHEET_URL %}
         <link rel="stylesheet" type="text/css" href="{{ STYLESHEET_URL }}" />
       {% endif %}