diff --git a/src/editors/automerge/livePreview/codeDecoration.ts b/src/editors/automerge/livePreview/codeDecoration.ts
index 6279b22..ad01186 100644
--- a/src/editors/automerge/livePreview/codeDecoration.ts
+++ b/src/editors/automerge/livePreview/codeDecoration.ts
@@ -86,11 +86,13 @@ export function buildCodeDecorations(
         if (node.name === 'FencedCode') {
           const endPos = Math.min(node.to, state.doc.length);
           const startLine = state.doc.lineAt(node.from).number;
-          let endLine = state.doc.lineAt(endPos).number;
-          // Trailing newline: don't paint the empty line after the block.
-          if (endPos === state.doc.lineAt(endPos).from && endLine > startLine) {
-            endLine--;
-          }
+          // Paint every line the node spans. @lezer/markdown excludes the
+          // trailing newline from a *closed* block, so node.to always lands on
+          // the closing-fence line and we never over-paint the blank line
+          // after it. For an *unterminated* block (still being typed) node.to
+          // includes the newline just added by Enter, so this correctly keeps
+          // the active empty line inside the block instead of dropping it.
+          const endLine = state.doc.lineAt(endPos).number;
           for (let l = startLine; l <= endLine; l++) {
             const line = state.doc.line(l);
             out.push(
diff --git a/src/editors/automerge/livePreview/livePreview.test.ts b/src/editors/automerge/livePreview/livePreview.test.ts
index 9ad066c..0cf45e2 100644
--- a/src/editors/automerge/livePreview/livePreview.test.ts
+++ b/src/editors/automerge/livePreview/livePreview.test.ts
@@ -186,6 +186,27 @@ describe('codeDecoration', () => {
     expect(withClass(list, 'cm-codeblock').length).toBeGreaterThanOrEqual(3);
     expect(withClass(list, 'cm-inline-formatting-hidden')).toHaveLength(0);
   });
+
+  it('paints the active empty line of an unterminated block (after Enter)', () => {
+    // "```js\n" — opening fence then Enter; the new line 2 is where the
+    // cursor sits and must be inside the block.
+    const state = makeState('```js\n', 6);
+    const lines = withClass(
+      decos(state, buildCodeDecorations(state)),
+      'cm-codeblock',
+    );
+    expect(lines).toHaveLength(2); // fence line + the new empty line
+  });
+
+  it('does not paint the blank line after a closed block', () => {
+    const state = makeState('```js\ncode\n```\n\nafter', 0);
+    const lines = withClass(
+      decos(state, buildCodeDecorations(state)),
+      'cm-codeblock',
+    );
+    // Exactly the three block lines (open fence, code, close fence).
+    expect(lines).toHaveLength(3);
+  });
 });
 
 describe('linkDecoration', () => {