diff --git a/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/mapping/PersistentEntitiesResourceMappings.java b/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/mapping/PersistentEntitiesResourceMappings.java
index 3d20052bb..76cbd39ab 100644
--- a/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/mapping/PersistentEntitiesResourceMappings.java
+++ b/spring-data-rest-core/src/main/java/org/springframework/data/rest/core/mapping/PersistentEntitiesResourceMappings.java
@@ -152,12 +152,7 @@ public class PersistentEntitiesResourceMappings implements ResourceMappings {
 	 */
 	@Override
 	public boolean hasMappingFor(Class<?> type) {
-
-		if (cache.containsKey(type)) {
-			return true;
-		}
-
-		return false;
+		return cache.get(ProxyUtils.getUserClass(type)) != null;
 	}
 
 	/*
diff --git a/spring-data-rest-core/src/test/java/org/springframework/data/rest/core/mapping/PersistentEntitiesResourceMappingsUnitTests.java b/spring-data-rest-core/src/test/java/org/springframework/data/rest/core/mapping/PersistentEntitiesResourceMappingsUnitTests.java
new file mode 100644
index 000000000..59cf88155
--- /dev/null
+++ b/spring-data-rest-core/src/test/java/org/springframework/data/rest/core/mapping/PersistentEntitiesResourceMappingsUnitTests.java
@@ -0,0 +1,42 @@
+/*
+ * Copyright 2018 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.rest.core.mapping;
+
+import static org.assertj.core.api.Assertions.*;
+
+import org.junit.Test;
+import org.springframework.data.keyvalue.core.mapping.context.KeyValueMappingContext;
+import org.springframework.data.mapping.context.PersistentEntities;
+
+/**
+ * Unit tests for {@link PersistentEntitiesResourceMappings}.
+ *
+ * @author Oliver Gierke
+ */
+public class PersistentEntitiesResourceMappingsUnitTests {
+
+	@Test // DATAREST-1320
+	public void doesNotConsiderCachedNullValuesToIndicateMappingAvailable() {
+
+		KeyValueMappingContext<?, ?> context = new KeyValueMappingContext<>();
+
+		PersistentEntitiesResourceMappings mappings = new PersistentEntitiesResourceMappings(
+				PersistentEntities.of(context));
+
+		assertThat(mappings.getMetadataFor(String.class)).isNull();
+		assertThat(mappings.hasMappingFor(String.class)).isFalse();
+	}
+}