diff --git a/spring-binding/src/main/java/org/springframework/binding/expression/el/ELExpressionParser.java b/spring-binding/src/main/java/org/springframework/binding/expression/el/ELExpressionParser.java
index 539f6073..a015062b 100644
--- a/spring-binding/src/main/java/org/springframework/binding/expression/el/ELExpressionParser.java
+++ b/spring-binding/src/main/java/org/springframework/binding/expression/el/ELExpressionParser.java
@@ -70,6 +70,7 @@ public class ELExpressionParser implements ExpressionParser {
 	 * @param conversionService the conversion service to use
 	 */
 	public void setConversionService(ConversionService conversionService) {
+		Assert.notNull(conversionService, "The conversion service is required");
 		this.conversionService = conversionService;
 	}