diff --git a/packages/apps/client/src/components/ScriptEditor/plugins/updateModel.ts b/packages/apps/client/src/components/ScriptEditor/plugins/updateModel.ts
index 2681c89..ebe828f 100644
--- a/packages/apps/client/src/components/ScriptEditor/plugins/updateModel.ts
+++ b/packages/apps/client/src/components/ScriptEditor/plugins/updateModel.ts
@@ -1,11 +1,12 @@
 import { Plugin } from 'prosemirror-state'
 import { UILineId } from '../../model/UILine'
 import { Node } from 'prosemirror-model'
+import { AddMarkStep, RemoveMarkStep, StepMap } from 'prosemirror-transform'
 import { schema } from '../scriptSchema'
 
 export const EXTERNAL_STATE_CHANGE = 'externalStateChange'
 
-export function updateModel(onChange?: (lineId: UILineId, contents: SomeContents) => void) {
+export function updateModel(onChange?: (lineId: UILineId, lineNodes: Node[]) => void) {
 	return new Plugin({
 		appendTransaction: (trs, oldState, newState) => {
 			const anyChanges = trs.reduce<boolean>((memo, tr) => memo || tr.docChanged, false)
@@ -14,7 +15,13 @@ export function updateModel(onChange?: (lineId: UILineId, contents: SomeContents
 			for (const tr of trs) {
 				if (tr.getMeta(EXTERNAL_STATE_CHANGE)) return
 				for (const step of tr.steps) {
-					step.getMap().forEach((oldStart, oldEnd, newStart, newEnd) => {
+					let stepMap = step.getMap()
+					// For some reason AddMarkStep/RemoveMarkStep don't provide a map. Generate it manually
+					if (step instanceof AddMarkStep || step instanceof RemoveMarkStep) {
+						stepMap = new StepMap([step.from, step.to - step.from, step.to - step.from])
+					}
+
+					stepMap.forEach((oldStart, oldEnd, newStart, newEnd) => {
 						oldState.doc.nodesBetween(oldStart, oldEnd, (_node, _pos, parent) => {
 							if (!parent) return
 							if (parent.type.name !== 'line') return
@@ -42,5 +49,3 @@ export function updateModel(onChange?: (lineId: UILineId, contents: SomeContents
 		},
 	})
 }
-
-type SomeContents = unknown