diff --git a/packages/super-editor/src/core/extensions/editable.js b/packages/super-editor/src/core/extensions/editable.js
index 2f0ce45251..d514327511 100644
--- a/packages/super-editor/src/core/extensions/editable.js
+++ b/packages/super-editor/src/core/extensions/editable.js
@@ -1,6 +1,32 @@
 import { Plugin, PluginKey } from 'prosemirror-state';
 import { Extension } from '../Extension.js';
 
+const handleBackwardReplaceInsertText = (view, event) => {
+  const isInsertTextInput = event?.inputType === 'insertText';
+  const hasTextData = typeof event?.data === 'string' && event.data.length > 0;
+  const hasNonEmptySelection = !view.state.selection.empty;
+
+  if (!isInsertTextInput || !hasTextData || !hasNonEmptySelection) {
+    return false;
+  }
+
+  const selection = view.state.selection;
+  const anchor = selection.anchor ?? selection.from;
+  const head = selection.head ?? selection.to;
+  const isBackwardSelection = anchor > head;
+
+  if (!isBackwardSelection) {
+    return false;
+  }
+
+  const tr = view.state.tr.insertText(event.data, selection.from, selection.to);
+  tr.setMeta('inputType', 'insertText');
+  view.dispatch(tr);
+  event.preventDefault();
+
+  return true;
+};
+
 /**
  * Editable extension controls whether the editor accepts user input.
  *
@@ -22,11 +48,17 @@ export const Editable = Extension.create({
       props: {
         editable: () => editor.options.editable,
         handleDOMEvents: {
-          beforeinput: (_view, event) => {
+          beforeinput: (view, event) => {
             if (!editor.options.editable) {
               event.preventDefault();
               return true;
             }
+
+            // Backward (right-to-left) replacement can be misinterpreted downstream as
+            // deleteContentBackward. Handle this narrow case explicitly at beforeinput level.
+            if (handleBackwardReplaceInsertText(view, event)) {
+              return true;
+            }
             return false;
           },
           mousedown: (_view, event) => {
diff --git a/packages/super-editor/src/core/extensions/editable.test.js b/packages/super-editor/src/core/extensions/editable.test.js
new file mode 100644
index 0000000000..40d5a6056d
--- /dev/null
+++ b/packages/super-editor/src/core/extensions/editable.test.js
@@ -0,0 +1,50 @@
+import { afterEach, describe, expect, it } from 'vitest';
+import { TextSelection } from 'prosemirror-state';
+import { initTestEditor } from '@tests/helpers/helpers.js';
+
+const findTextRange = (doc, text) => {
+  let range = null;
+  doc.descendants((node, pos) => {
+    if (node.isText && node.text === text) {
+      range = {
+        from: pos,
+        to: pos + node.text.length,
+      };
+      return false;
+    }
+    return true;
+  });
+  return range;
+};
+
+describe('Editable extension backward replace handling', () => {
+  let editor = null;
+
+  afterEach(() => {
+    editor?.destroy();
+    editor = null;
+  });
+
+  it('replaces backward non-empty selection on beforeinput insertText', () => {
+    ({ editor } = initTestEditor({
+      mode: 'text',
+      content: '<p>PREAMBLE</p>',
+    }));
+
+    const range = findTextRange(editor.state.doc, 'PREAMBLE');
+    expect(range).not.toBeNull();
+
+    const backwardSelection = TextSelection.create(editor.state.doc, range.to, range.from);
+    editor.view.dispatch(editor.state.tr.setSelection(backwardSelection));
+
+    const beforeInputEvent = new InputEvent('beforeinput', {
+      data: 'Z',
+      inputType: 'insertText',
+      bubbles: true,
+      cancelable: true,
+    });
+    editor.view.dom.dispatchEvent(beforeInputEvent);
+
+    expect(editor.state.doc.textContent).toBe('Z');
+  });
+});
diff --git a/tests/behavior/tests/formatting/replace-text-preserves-style.spec.ts b/tests/behavior/tests/formatting/replace-text-preserves-style.spec.ts
new file mode 100644
index 0000000000..6e1be363e3
--- /dev/null
+++ b/tests/behavior/tests/formatting/replace-text-preserves-style.spec.ts
@@ -0,0 +1,86 @@
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { test, expect } from '../../fixtures/superdoc.js';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const DOC_PATH = path.resolve(__dirname, '../../test-data/basic/sd-site-doc-2026.docx');
+
+test.skip(!fs.existsSync(DOC_PATH), 'Test document not available — run pnpm corpus:pull');
+
+/**
+ * SD-1951: Highlighting text right-to-left (backward selection) and typing a
+ * replacement should preserve the original text's styling. On main this was
+ * broken because the backward selection caused ProseMirror to misinterpret the
+ * insertText input as deleteContentBackward.
+ */
+test('backward-selected text replacement preserves original style (SD-1951)', async ({ superdoc }) => {
+  await superdoc.loadDocument(DOC_PATH);
+  await superdoc.waitForStable();
+
+  const titleText = 'Mutual Agreement for Document Excellence';
+  await superdoc.assertTextContains(titleText);
+
+  // Capture the title's marks before replacement
+  const titleStart = await superdoc.findTextPos(titleText);
+  const titleEnd = titleStart + titleText.length;
+  const originalMarks = await superdoc.getMarkAttrsAtPos(titleStart);
+
+  // Create a BACKWARD selection (right-to-left) and dispatch a beforeinput
+  // event to simulate typing. This exercises the exact code path from the
+  // SD-1951 fix: the editable extension's beforeinput handler intercepts
+  // backward selection + insertText and replaces text with correct marks.
+  //
+  // We dispatch via view.dom so ProseMirror's event pipeline processes it
+  // naturally through runCustomHandler → handleDOMEvents → our handler.
+  const result = await superdoc.page.evaluate(
+    ({ from, to }) => {
+      const { state, view } = (window as any).editor;
+      const TextSelectionClass = state.selection.constructor;
+      const backward = TextSelectionClass.create(state.doc, to, from);
+      view.dispatch(state.tr.setSelection(backward));
+
+      // Dispatch a native beforeinput event on view.dom
+      const event = new InputEvent('beforeinput', {
+        inputType: 'insertText',
+        data: 'Z',
+        bubbles: true,
+        cancelable: true,
+      });
+      view.dom.dispatchEvent(event);
+
+      return {
+        prevented: event.defaultPrevented,
+        docText: (window as any).editor.state.doc.textContent.substring(0, 80),
+      };
+    },
+    { from: titleStart, to: titleEnd },
+  );
+  await superdoc.waitForStable();
+
+  // On the fix branch, the handler intercepts and replaces text (preventDefault).
+  // On main, the handler doesn't intercept backward selection + insertText.
+  expect(result.prevented).toBe(true);
+  expect(result.docText).toContain('Z');
+  expect(result.docText).not.toContain(titleText);
+
+  // The replacement character must appear in the document
+  await superdoc.assertTextContains('Z');
+  await superdoc.assertTextNotContains(titleText);
+
+  // The replacement must retain the original title's marks (font family, size),
+  // not inherit from the previous paragraph or document defaults.
+  const zPos = await superdoc.findTextPos('Z');
+  const replacementMarks = await superdoc.getMarkAttrsAtPos(zPos);
+
+  const getTextStyleAttrs = (marks: Array<{ name: string; attrs: Record<string, unknown> }>) =>
+    marks.find((m) => m.name === 'textStyle')?.attrs;
+
+  const originalStyle = getTextStyleAttrs(originalMarks);
+  const replacementStyle = getTextStyleAttrs(replacementMarks);
+
+  expect(originalStyle).toBeDefined();
+  expect(replacementStyle).toBeDefined();
+  expect(replacementStyle!.fontFamily).toBe(originalStyle!.fontFamily);
+  expect(replacementStyle!.fontSize).toBe(originalStyle!.fontSize);
+});