diff --git a/src/main/java/org/springframework/hateoas/IanaLinkRelations.java b/src/main/java/org/springframework/hateoas/IanaLinkRelations.java
index 259a2550..ebd058bc 100644
--- a/src/main/java/org/springframework/hateoas/IanaLinkRelations.java
+++ b/src/main/java/org/springframework/hateoas/IanaLinkRelations.java
@@ -784,6 +784,8 @@ public class IanaLinkRelations {
 	 */
 	public static boolean isIanaRel(LinkRelation relation) {
 
+		Assert.notNull(relation, "Link relation must not be null!");
+
 		return LINK_RELATIONS.stream() //
 				.anyMatch(it -> it.value().equalsIgnoreCase(relation.value()));
 
diff --git a/src/test/java/org/springframework/hateoas/IanaLinkRelationUnitTest.java b/src/test/java/org/springframework/hateoas/IanaLinkRelationUnitTest.java
index 3ba1463d..90bf2306 100644
--- a/src/test/java/org/springframework/hateoas/IanaLinkRelationUnitTest.java
+++ b/src/test/java/org/springframework/hateoas/IanaLinkRelationUnitTest.java
@@ -40,8 +40,8 @@ public class IanaLinkRelationUnitTest {
 	@Test
 	public void testingForOfficialIanaLinkRelation() {
 
-		assertThat(IanaLinkRelations.isIanaRel((String) null)).isFalse();
-		assertThat(IanaLinkRelations.isIanaRel((LinkRelation) null)).isFalse();
+		assertThatIllegalArgumentException().isThrownBy(() -> IanaLinkRelations.isIanaRel((String) null));
+		assertThatIllegalArgumentException().isThrownBy(() -> IanaLinkRelations.isIanaRel((LinkRelation) null));
 		assertThat(IanaLinkRelations.isIanaRel("")).isFalse();
 		assertThat(IanaLinkRelations.isIanaRel("foo-bar")).isFalse();