diff --git a/code/ui/blocks/src/blocks/Source.stories.tsx b/code/ui/blocks/src/blocks/Source.stories.tsx
index ffd2eb90db0e..00a9ea2d3741 100644
--- a/code/ui/blocks/src/blocks/Source.stories.tsx
+++ b/code/ui/blocks/src/blocks/Source.stories.tsx
@@ -78,6 +78,11 @@ export const Code: Story = {
   args: { code },
 };
 
+export const CodeUnattached: Story = {
+  args: { code },
+  parameters: { attached: false },
+};
+
 export const CodeParameters: Story = {
   args: { of: ParametersStories.Code },
 };
diff --git a/code/ui/blocks/src/blocks/Source.tsx b/code/ui/blocks/src/blocks/Source.tsx
index f63d497af048..4957ad5aa55b 100644
--- a/code/ui/blocks/src/blocks/Source.tsx
+++ b/code/ui/blocks/src/blocks/Source.tsx
@@ -114,10 +114,16 @@ export const useSourceProps = (
     const resolved = docsContext.resolveOf(props.of, ['story']);
     stories = [resolved.story];
   } else if (stories.length === 0) {
-    stories = [docsContext.storyById()];
+    try {
+      // Always fall back to the primary story for source parameters, even if code is set.
+      stories = [docsContext.storyById()];
+    } catch (err) {
+      // You are allowed to use <Story code="..." /> unattached.
+      if (!props.code) throw err;
+    }
   }
 
-  const sourceParameters = (stories[0].parameters.docs?.source || {}) as SourceParameters;
+  const sourceParameters = (stories[0]?.parameters?.docs?.source || {}) as SourceParameters;
   let { code } = props; // We will fall back to `sourceParameters.code`, but per story below
   let format = props.format ?? sourceParameters.format;
   const language = props.language ?? sourceParameters.language ?? 'jsx';