diff --git a/src/lib/components/common/DiffEditorModal.svelte b/src/lib/components/common/DiffEditorModal.svelte
index 6f14bc331a..03e61df49e 100644
--- a/src/lib/components/common/DiffEditorModal.svelte
+++ b/src/lib/components/common/DiffEditorModal.svelte
@@ -3,7 +3,7 @@
 	import { getContext } from 'svelte';
 	import { copyToClipboard } from '$lib/utils';
 	import { basicSetup, EditorView } from 'codemirror';
-	import { Compartment } from '@codemirror/state';
+	import { Compartment, type Text } from '@codemirror/state';
 	import { keymap, type ViewUpdate } from '@codemirror/view';
 	import { indentWithTab, isolateHistory } from '@codemirror/commands';
 	import { LanguageDescription, indentUnit } from '@codemirror/language';
@@ -14,7 +14,7 @@
 	import ConfirmDialog from './ConfirmDialog.svelte';
 	import FileCodeEditor from '$lib/components/chat/FileNav/FileCodeEditor.svelte';
 	import XMark from '$lib/components/icons/XMark.svelte';
-	import { lineAlignment, alignChangedLines } from './diffEditorAlignment';
+	import { lineAlignment, alignChangedLines, clearLineAlignment } from './diffEditorAlignment';
 	import {
 		copyChunk,
 		selectedChunk,
@@ -181,6 +181,8 @@
 		let view: MergeView | null = null;
 		let observer: MutationObserver | undefined;
 		let alignmentFrame = 0;
+		let alignmentDocuments: readonly [Text, Text] | null = null;
+		let alignmentGeometry = '';
 		const themes = [new Compartment(), new Compartment()];
 		const language = [new Compartment(), new Compartment()];
 		const path = session?.path;
@@ -208,7 +210,22 @@
 					alignmentFrame = requestAnimationFrame(() => {
 						alignmentFrame = 0;
 						if (!disposed && view) {
-							alignChangedLines(view.a, view.b, view.chunks);
+							const documents = [view.a.state.doc, view.b.state.doc] as const;
+							const geometry = [
+								view.a.contentDOM.clientWidth,
+								view.b.contentDOM.clientWidth,
+								view.a.defaultLineHeight,
+								view.b.defaultLineHeight
+							].join(':');
+							const reset =
+								alignmentDocuments &&
+								(alignmentDocuments[0] !== documents[0] ||
+									alignmentDocuments[1] !== documents[1] ||
+									geometry !== alignmentGeometry);
+							alignmentDocuments = documents;
+							alignmentGeometry = geometry;
+							if (!reset || !clearLineAlignment(view.a, view.b))
+								alignChangedLines(view.a, view.b, view.chunks);
 							view.reconfigure({});
 						}
 					});
diff --git a/src/lib/components/common/diffEditorAlignment.ts b/src/lib/components/common/diffEditorAlignment.ts
index 80e5d568a4..3fb30c1a6b 100644
--- a/src/lib/components/common/diffEditorAlignment.ts
+++ b/src/lib/components/common/diffEditorAlignment.ts
@@ -30,11 +30,22 @@ export const lineAlignment = StateField.define<DecorationSet>({
 	create: () => Decoration.none,
 	update: (value, transaction) => {
 		for (const effect of transaction.effects) if (effect.is(setSpacers)) return effect.value;
-		return value.map(transaction.changes);
+		return transaction.docChanged ? Decoration.none : value;
 	},
 	provide: (field) => EditorView.decorations.from(field)
 });
 
+export function clearLineAlignment(a: EditorView, b: EditorView) {
+	let changed = false;
+	for (const view of [a, b]) {
+		if (view.state.field(lineAlignment).size) {
+			view.dispatch({ effects: setSpacers.of(Decoration.none) });
+			changed = true;
+		}
+	}
+	return changed;
+}
+
 // Only remeasure paired rows present in both virtualized viewports. Recomputing
 // offscreen spacers from estimated heights would move already aligned content.
 export function alignChangedLines(a: EditorView, b: EditorView, chunks: readonly Chunk[]) {