diff --git a/src/validators/edition-group.ts b/src/validators/edition-group.ts
index 6785560e..2f5db9d8 100644
--- a/src/validators/edition-group.ts
+++ b/src/validators/edition-group.ts
@@ -29,6 +29,7 @@ import {
 } from './common';
 
 import type {IdentifierTypeWithIdT} from '../types/identifiers';
+import {Iterable} from 'immutable';
 import _ from 'lodash';
 import {isIterable} from '../util';
 
@@ -52,8 +53,13 @@ export function validateEditionGroup(
 		validateAuthorCreditSectionMerge(get(formData, 'authorCredit', {}));
 	}
 	else if (!authorCreditEnable) {
-		const emptyAuthorCredit = isIterable(formData) ? formData.get('authorCreditEditor')?.size === 0 :
-			_.size(get(formData, 'authorCreditEditor', {})) === 0;
+		let emptyAuthorCredit:boolean;
+		if (isIterable(formData)) {
+			emptyAuthorCredit = (formData.get('authorCreditEditor') as Iterable<unknown, unknown>)?.size === 0;
+		}
+		else {
+			emptyAuthorCredit = _.size(get(formData, 'authorCreditEditor', {})) === 0;
+		}
 		if (!emptyAuthorCredit) {
 			throw new ValidationError('Disabled author credit has to be empty', 'authorCreditEditor');
 		}
diff --git a/src/validators/edition.ts b/src/validators/edition.ts
index 8ad166f4..07df52dc 100644
--- a/src/validators/edition.ts
+++ b/src/validators/edition.ts
@@ -33,6 +33,7 @@ import {ValidationError, get, validateDate, validatePositiveInteger, validateUUI
 import {convertMapToObject, isIterable} from '../util';
 
 import {IdentifierTypeWithIdT} from '../types/identifiers';
+import {Iterable} from 'immutable';
 import _ from 'lodash';
 
 
@@ -127,8 +128,13 @@ export function validateEdition(
 		validateAuthorCreditSectionMerge(get(formData, 'authorCredit', {}));
 	}
 	else if (!authorCreditEnable) {
-		const emptyAuthorCredit = isIterable(formData) ? formData.get('authorCreditEditor')?.size === 0 :
-			_.size(get(formData, 'authorCreditEditor', {})) === 0;
+		let emptyAuthorCredit:boolean;
+		if (isIterable(formData)) {
+			emptyAuthorCredit = (formData.get('authorCreditEditor') as Iterable<unknown, unknown>)?.size === 0;
+		}
+		else {
+			emptyAuthorCredit = _.size(get(formData, 'authorCreditEditor', {})) === 0;
+		}
 		if (!emptyAuthorCredit) {
 			throw new ValidationError('Disabled author credit has to be empty', 'authorCreditEditor');
 		}