diff --git a/src/Document.ts b/src/Document.ts
index 38988392..df0bf3cd 100644
--- a/src/Document.ts
+++ b/src/Document.ts
@@ -12,7 +12,7 @@ export interface DocumentConstructorOptions {
 }
 
 export interface BuildForeignKeyDefinitionsResult {
-	filename: string;
+	filename: string[];
 	entityName: string;
 	entityIds: string[];
 }
@@ -130,8 +130,8 @@ class Document {
 			return [];
 		}
 
-		// U2 does not allow commas in filenames so we can use it to separate filename/entityName combinations
-		const separator = ',';
+		// U2 does not allow pound signs in filenames so we can use it to separate filename/entityName combinations
+		const separator = '#';
 		const definitionMap = Array.from(this.#schema.paths).reduce(
 			(foreignKeyDefinitions, [keyPath, schemaType]) => {
 				const value = getIn(this, keyPath, null);
@@ -165,8 +165,11 @@ class Document {
 		return Array.from(definitionMap).reduce<BuildForeignKeyDefinitionsResult[]>(
 			(acc, [key, value]) => {
 				const keyParts = key.split(separator);
-				const filename = keyParts[0];
-				// Just incase the entity name included a comma, rejoin
+				const fileName = keyParts[0];
+				// If an array of filenames was provided, when we transformed the array into a string above, commas
+				// would have been inserted between each filename. Split the string back into an array.
+				const filename = fileName.split(',');
+				// Just incase the entity name included a pound sign, rejoin
 				const entityName = keyParts.slice(1).join(separator);
 				acc.push({ filename, entityName, entityIds: Array.from(value) });
 				return acc;
diff --git a/src/__tests__/Document.test.ts b/src/__tests__/Document.test.ts
index c9a699a8..929ec51c 100644
--- a/src/__tests__/Document.test.ts
+++ b/src/__tests__/Document.test.ts
@@ -652,7 +652,7 @@ describe('buildForeignKeyDefinitions', () => {
 		const document = new DocumentSubclass(schema, { data: { prop1: 'foo' } });
 
 		const expected: BuildForeignKeyDefinitionsResult[] = [
-			{ filename: 'FILE', entityName: 'entityName', entityIds: ['foo'] },
+			{ filename: ['FILE'], entityName: 'entityName', entityIds: ['foo'] },
 		];
 		expect(document.buildForeignKeyDefinitions()).toEqual(expected);
 	});
@@ -675,8 +675,8 @@ describe('buildForeignKeyDefinitions', () => {
 		const document = new DocumentSubclass(schema, { data: { prop1: 'foo', prop2: 'bar' } });
 
 		const expected: BuildForeignKeyDefinitionsResult[] = [
-			{ filename: 'FILE1', entityName: 'entityName1', entityIds: ['foo'] },
-			{ filename: 'FILE2', entityName: 'entityName2', entityIds: ['bar'] },
+			{ filename: ['FILE1'], entityName: 'entityName1', entityIds: ['foo'] },
+			{ filename: ['FILE2'], entityName: 'entityName2', entityIds: ['bar'] },
 		];
 		expect(document.buildForeignKeyDefinitions()).toEqual(expected);
 	});
@@ -691,7 +691,7 @@ describe('buildForeignKeyDefinitions', () => {
 		const document = new DocumentSubclass(schema, { data: { prop1: 'foo', prop2: 'bar' } });
 
 		const expected: BuildForeignKeyDefinitionsResult[] = [
-			{ filename: 'FILE', entityName: 'entityName', entityIds: ['foo', 'bar'] },
+			{ filename: ['FILE'], entityName: 'entityName', entityIds: ['foo', 'bar'] },
 		];
 		expect(document.buildForeignKeyDefinitions()).toEqual(expected);
 	});
@@ -707,7 +707,7 @@ describe('buildForeignKeyDefinitions', () => {
 		const document = new DocumentSubclass(schema, { data: { prop1: ['foo', 'bar'] } });
 
 		const expected: BuildForeignKeyDefinitionsResult[] = [
-			{ filename: 'FILE', entityName: 'entityName', entityIds: ['foo', 'bar'] },
+			{ filename: ['FILE'], entityName: 'entityName', entityIds: ['foo', 'bar'] },
 		];
 		expect(document.buildForeignKeyDefinitions()).toEqual(expected);
 	});
@@ -741,8 +741,8 @@ describe('buildForeignKeyDefinitions', () => {
 		});
 
 		const expected: BuildForeignKeyDefinitionsResult[] = [
-			{ filename: 'FILE1', entityName: 'entityName', entityIds: ['foo', 'baz'] },
-			{ filename: 'FILE2', entityName: 'entityName', entityIds: ['bar', 'qux'] },
+			{ filename: ['FILE1'], entityName: 'entityName', entityIds: ['foo', 'baz'] },
+			{ filename: ['FILE2'], entityName: 'entityName', entityIds: ['bar', 'qux'] },
 		];
 		expect(document.buildForeignKeyDefinitions()).toEqual(expected);
 	});
@@ -758,7 +758,25 @@ describe('buildForeignKeyDefinitions', () => {
 		const document = new DocumentSubclass(schema, { data: { _id: 'id', prop1: 'foo' } });
 
 		const expected: BuildForeignKeyDefinitionsResult[] = [
-			{ filename: 'FILE', entityName: 'entityName', entityIds: ['id'] },
+			{ filename: ['FILE'], entityName: 'entityName', entityIds: ['id'] },
+		];
+		expect(document.buildForeignKeyDefinitions()).toEqual(expected);
+	});
+
+	test('should build foreign key definitions with multiple filenames', () => {
+		const definition: SchemaDefinition = {
+			prop1: {
+				type: 'string',
+				path: '1',
+				foreignKey: { entityName: 'entityName', file: ['FILE1', 'FILE2'] },
+			},
+		};
+		const schema = new Schema(definition);
+
+		const document = new DocumentSubclass(schema, { data: { prop1: 'foo' } });
+
+		const expected: BuildForeignKeyDefinitionsResult[] = [
+			{ filename: ['FILE1', 'FILE2'], entityName: 'entityName', entityIds: ['foo'] },
 		];
 		expect(document.buildForeignKeyDefinitions()).toEqual(expected);
 	});
diff --git a/src/__tests__/compileModel.test.ts b/src/__tests__/compileModel.test.ts
index f3f0cea7..01357d8d 100644
--- a/src/__tests__/compileModel.test.ts
+++ b/src/__tests__/compileModel.test.ts
@@ -690,7 +690,7 @@ describe('save', () => {
 				__v: null,
 				record: `prop1-value${am}123`,
 				foreignKeyDefinitions: [
-					{ entityIds: ['prop1-value'], entityName: 'prop1', filename: 'FK_FILE' },
+					{ entityIds: ['prop1-value'], entityName: 'prop1', filename: ['FK_FILE'] },
 				],
 			},
 			{},
@@ -723,7 +723,7 @@ describe('save', () => {
 					__v: null,
 					record: `prop1-value${am}123`,
 					foreignKeyDefinitions: [
-						{ entityIds: ['prop1-value'], entityName: 'prop1', filename: 'FK_FILE' },
+						{ entityIds: ['prop1-value'], entityName: 'prop1', filename: ['FK_FILE'] },
 					],
 				},
 				{},
@@ -934,7 +934,7 @@ describe('save', () => {
 					__v: null,
 					record: `prop1-value${am}123`,
 					foreignKeyDefinitions: [
-						{ entityIds: ['prop1-value'], entityName: 'prop1', filename: 'FK_FILE' },
+						{ entityIds: ['prop1-value'], entityName: 'prop1', filename: ['FK_FILE'] },
 					],
 				},
 				{ maxReturnPayloadSize, userDefined, requestId },
diff --git a/src/schemaType/__tests__/DocumentArrayType.test.ts b/src/schemaType/__tests__/DocumentArrayType.test.ts
index 40923774..8feaf077 100644
--- a/src/schemaType/__tests__/DocumentArrayType.test.ts
+++ b/src/schemaType/__tests__/DocumentArrayType.test.ts
@@ -308,8 +308,8 @@ describe('transformForeignKeyDefinitionsToDb', () => {
 		value2.prop2 = 4.56;
 
 		const expected: ForeignKeyDbDefinition[] = [
-			{ filename: 'FILE', entityId: 'foo', entityName: 'FK_ENTITY' },
-			{ filename: 'FILE', entityId: 'bar', entityName: 'FK_ENTITY' },
+			{ filename: ['FILE'], entityId: 'foo', entityName: 'FK_ENTITY' },
+			{ filename: ['FILE'], entityId: 'bar', entityName: 'FK_ENTITY' },
 		];
 		expect(documentArrayType.transformForeignKeyDefinitionsToDb([value1, value2])).toEqual(
 			expected,