diff --git a/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/file/builder/FlatFileItemReaderBuilder.java b/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/file/builder/FlatFileItemReaderBuilder.java
index ab8601b18c..e52d4dbde9 100644
--- a/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/file/builder/FlatFileItemReaderBuilder.java
+++ b/spring-batch-infrastructure/src/main/java/org/springframework/batch/item/file/builder/FlatFileItemReaderBuilder.java
@@ -58,6 +58,8 @@
  * @author Glenn Renfro
  * @author Mahmoud Ben Hassine
  * @author Drummond Dawson
+ * @author Patrick Baumgartner
+ * @author François Martin
  * @since 4.0
  * @see FlatFileItemReader
  */
@@ -459,6 +461,9 @@ else if (this.delimitedBuilder != null) {
 				throw new IllegalStateException("No LineTokenizer implementation was provided.");
 			}
 
+			Assert.state(this.targetType == null || this.fieldSetMapper == null,
+					"Either a TargetType or FieldSetMapper can be set, can't be both.");
+
 			if (this.targetType != null || StringUtils.hasText(this.prototypeBeanName)) {
 				if (this.targetType != null && this.targetType.isRecord()) {
 					RecordFieldSetMapper<T> mapper = new RecordFieldSetMapper<>(this.targetType);
diff --git a/spring-batch-infrastructure/src/test/java/org/springframework/batch/item/file/builder/FlatFileItemReaderBuilderTests.java b/spring-batch-infrastructure/src/test/java/org/springframework/batch/item/file/builder/FlatFileItemReaderBuilderTests.java
index d1890ef383..e64ec68e5d 100644
--- a/spring-batch-infrastructure/src/test/java/org/springframework/batch/item/file/builder/FlatFileItemReaderBuilderTests.java
+++ b/spring-batch-infrastructure/src/test/java/org/springframework/batch/item/file/builder/FlatFileItemReaderBuilderTests.java
@@ -56,6 +56,8 @@
  * @author Mahmoud Ben Hassine
  * @author Drummond Dawson
  * @author Glenn Renfro
+ * @author Patrick Baumgartner
+ * @author François Martin
  */
 class FlatFileItemReaderBuilderTests {
 
@@ -563,6 +565,17 @@ void testErrorMessageWhenNoLineTokenizerWasProvided() {
 		}
 	}
 
+	@Test
+	void testErrorWhenTargetTypeAndFieldSetMapperIsProvided() {
+		var builder = new FlatFileItemReaderBuilder<Foo>().name("fooReader")
+			.resource(getResource("1;2;3"))
+			.lineTokenizer(line -> new DefaultFieldSet(line.split(";")))
+			.targetType(Foo.class)
+			.fieldSetMapper(fieldSet -> new Foo());
+		var exception = assertThrows(IllegalStateException.class, builder::build);
+		assertEquals("Either a TargetType or FieldSetMapper can be set, can't be both.", exception.getMessage());
+	}
+
 	@Test
 	void testSetupWithRecordTargetType() {
 		// given