diff --git a/src/vs/workbench/contrib/mergeEditor/browser/model.ts b/src/vs/workbench/contrib/mergeEditor/browser/model.ts
index 27329b56105..34c55925dad 100644
--- a/src/vs/workbench/contrib/mergeEditor/browser/model.ts
+++ b/src/vs/workbench/contrib/mergeEditor/browser/model.ts
@@ -9,6 +9,10 @@ import { Range } from 'vs/editor/common/core/range';
 import { ILineChange } from 'vs/editor/common/diff/diffComputer';
 import { ITextModel } from 'vs/editor/common/model';
 
+/**
+ * Represents an edit, expressed in whole lines:
+ * At {@link LineRange.startLineNumber}, delete {@link LineRange.lineCount} many lines and insert {@link newLines}.
+*/
 export class LineEdit {
 	constructor(
 		public readonly range: LineRange,
@@ -30,10 +34,26 @@ export class LineEdits {
 	public apply(model: ITextModel): void {
 		model.pushEditOperations(
 			null,
-			this.edits.map((e) => ({
-				range: new Range(e.range.startLineNumber, 1, e.range.endLineNumberExclusive, 1),
-				text: e.newLines.map(l => l + '\n').join(''),
-			})),
+			this.edits.map((e) => {
+				if (e.range.endLineNumberExclusive <= model.getLineCount()) {
+					return {
+						range: new Range(e.range.startLineNumber, 1, e.range.endLineNumberExclusive, 1),
+						text: e.newLines.map(s => s + '\n').join(''),
+					};
+				}
+
+				if (e.range.startLineNumber === 1) {
+					return {
+						range: new Range(1, 1, model.getLineCount(), Number.MAX_SAFE_INTEGER),
+						text: e.newLines.join('\n'),
+					};
+				}
+
+				return {
+					range: new Range(e.range.startLineNumber - 1, Number.MAX_SAFE_INTEGER, model.getLineCount(), Number.MAX_SAFE_INTEGER),
+					text: e.newLines.map(s => '\n' + s).join(''),
+				};
+			}),
 			() => null
 		);
 	}
@@ -110,6 +130,14 @@ export class LineRange {
 	public deltaEnd(delta: number): LineRange {
 		return new LineRange(this.startLineNumber, this.lineCount + delta);
 	}
+
+	public getLines(model: ITextModel): string[] {
+		const result = new Array(this.lineCount);
+		for (let i = 0; i < this.lineCount; i++) {
+			result[i] = model.getLineContent(this.startLineNumber + i);
+		}
+		return result;
+	}
 }
 
 export class LineDiff {
@@ -215,19 +243,11 @@ export class LineDiff {
 	}
 
 	private getModifiedLines(): string[] {
-		const result = new Array(this.modifiedRange.lineCount);
-		for (let i = 0; i < this.modifiedRange.lineCount; i++) {
-			result[i] = this.modifiedTextModel.getLineContent(this.modifiedRange.startLineNumber + i);
-		}
-		return result;
+		return this.modifiedRange.getLines(this.modifiedTextModel);
 	}
 
 	private getOriginalLines(): string[] {
-		const result = new Array(this.originalRange.lineCount);
-		for (let i = 0; i < this.originalRange.lineCount; i++) {
-			result[i] = this.originalTextModel.getLineContent(this.originalRange.startLineNumber + i);
-		}
-		return result;
+		return this.originalRange.getLines(this.originalTextModel);
 	}
 }