diff --git a/spring-graphql/src/main/java/org/springframework/graphql/data/method/annotation/support/AnnotatedControllerConfigurer.java b/spring-graphql/src/main/java/org/springframework/graphql/data/method/annotation/support/AnnotatedControllerConfigurer.java
index 9724c9bb..54da1058 100644
--- a/spring-graphql/src/main/java/org/springframework/graphql/data/method/annotation/support/AnnotatedControllerConfigurer.java
+++ b/spring-graphql/src/main/java/org/springframework/graphql/data/method/annotation/support/AnnotatedControllerConfigurer.java
@@ -132,7 +132,7 @@ public class AnnotatedControllerConfigurer
 	 */
 	@Deprecated
 	public void setConversionService(ConversionService conversionService) {
-		Assert.isInstanceOf(FormattingConversionService.class, "FormattingConversionService is required");
+		Assert.isInstanceOf(FormattingConversionService.class, conversionService);
 		this.conversionService = (FormattingConversionService) conversionService;
 	}