diff --git a/lib/files/src/SettingsXml.ts b/lib/files/src/SettingsXml.ts
index aa4b6e3..2441fac 100644
--- a/lib/files/src/SettingsXml.ts
+++ b/lib/files/src/SettingsXml.ts
@@ -34,6 +34,12 @@ export type SettingsI = {
 	footnoteProperties?: FootnoteProps | null;
 
 	documentProtection?: DocumentProtectionProps | null;
+
+	/**
+	 * Word compatibility mode version. Common values: 11 (2003), 12 (2007), 14 (2010), 15 (2013+).
+	 * Set to `null` to omit the compatibility block entirely.
+	 */
+	compatibilityMode?: 11 | 12 | 14 | 15 | null;
 };
 
 export type DocumentProtectionProps = {
@@ -54,6 +60,7 @@ const DEFAULT_SETTINGS: SettingsI = {
 	defaultTabStop: null,
 	footnoteProperties: null,
 	documentProtection: null,
+	compatibilityMode: null,
 };
 
 enum SettingType {
@@ -61,6 +68,7 @@ enum SettingType {
 	OnOff,
 	Relationship,
 	Formatting,
+	Custom,
 }
 
 type SettingMeta =
@@ -79,6 +87,11 @@ type SettingMeta =
 			ooxmlLocalName: string;
 			ooxmlType: SettingType.Formatting;
 	  }
+	| {
+			docxmlName: keyof SettingsI;
+			ooxmlLocalName: string;
+			ooxmlType: SettingType.Custom;
+	  }
 	| {
 			docxmlName: keyof SettingsI;
 			ooxmlLocalName: string;
@@ -117,6 +130,11 @@ const settingsMeta: Array<SettingMeta> = [
 		ooxmlLocalName: 'documentProtection',
 		ooxmlType: SettingType.OnOff,
 	},
+	{
+		docxmlName: 'compatibilityMode',
+		ooxmlLocalName: 'compat',
+		ooxmlType: SettingType.Custom,
+	},
 ];
 
 export class SettingsXml extends XmlFileWithContentTypes {
@@ -230,6 +248,13 @@ export class SettingsXml extends XmlFileWithContentTypes {
 					) else (),
 					if (exists($defaultTabStop)) then element ${QNS.w}defaultTabStop {
 						attribute ${QNS.w}val { $defaultTabStop('twip') }
+					} else (),
+					if (exists($compatibilityMode)) then element ${QNS.w}compat {
+						element ${QNS.w}compatSetting {
+							attribute ${QNS.w}name { "compatibilityMode" },
+							attribute ${QNS.w}uri { "http://schemas.microsoft.com/office/word" },
+							attribute ${QNS.w}val { $compatibilityMode }
+						}
 					} else ()
 				}
 			</w:settings>`,
@@ -290,8 +315,14 @@ export class SettingsXml extends XmlFileWithContentTypes {
 					} else map {
 						"enforcement": $enforcement
 					}
-				) else ()
+				) else (),
+				"compatibilityMode": let $cs := ./${QNS.w}compat/${QNS.w}compatSetting[
+					@${QNS.w}name = "compatibilityMode" and
+					@${QNS.w}uri = "http://schemas.microsoft.com/office/word"
+				]
+				return if ($cs) then number($cs/@${QNS.w}val) else ()
 			}`,
+
 			xml
 		);
 
diff --git a/lib/files/test/SettingsXml.test.ts b/lib/files/test/SettingsXml.test.ts
index 28f51a2..86e35f7 100644
--- a/lib/files/test/SettingsXml.test.ts
+++ b/lib/files/test/SettingsXml.test.ts
@@ -108,4 +108,41 @@ describe('SettingsXml', () => {
 			docxFromArchive.document.settings.get('documentProtection')
 		).toEqual(customSettings);
 	});
+
+	describe('compatibilityMode', () => {
+		it('compatibilityMode default is null', async () => {
+			const settings = new SettingsXml('test');
+			expect(settings.get('compatibilityMode')).toBe(null);
+			expect(serialize(await settings.$$$toNode())).toEqual(
+				`<w:settings xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"/>`
+			);
+		});
+		it('compatibilityMode set and get', async () => {
+			const settings = new SettingsXml('test');
+			settings.set('compatibilityMode', 15);
+			expect(settings.get('compatibilityMode')).toBe(15);
+			expect(serialize(await settings.$$$toNode())).toEqual(
+				`<w:settings xmlns:w="http://schemas.openxmlformats.org/wordprocessingml/2006/main"><w:compat><w:compatSetting w:name="compatibilityMode" w:uri="http://schemas.microsoft.com/office/word" w:val="15"/></w:compat></w:settings>`
+			);
+		});
+		it('compatibilityMode roundtrips through archive', async () => {
+			const docx = Docx.fromNothing();
+			docx.document.settings.set('compatibilityMode', 15);
+			const docxFromArchive = await Docx.fromArchive(
+				await docx.toArchive()
+			);
+			expect(
+				docxFromArchive.document.settings.get('compatibilityMode')
+			).toBe(15);
+		});
+		it('compatibilityMode null roundtrips through archive', async () => {
+			const docx = Docx.fromNothing();
+			const docxFromArchive = await Docx.fromArchive(
+				await docx.toArchive()
+			);
+			expect(
+				docxFromArchive.document.settings.get('compatibilityMode')
+			).toBe(null);
+		});
+	});
 });