diff --git a/spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/json/PersistentEntityJackson2Module.java b/spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/json/PersistentEntityJackson2Module.java
index d676264f3..6c4c5ccf8 100644
--- a/spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/json/PersistentEntityJackson2Module.java
+++ b/spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/json/PersistentEntityJackson2Module.java
@@ -763,7 +763,10 @@ public class PersistentEntityJackson2Module extends SimpleModule {
 		 */
 		@Override
 		public Object deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
-			return invoker.invokeFindById(p.getValueAsString());
+
+			Object id = p.getCurrentToken().isNumeric() ? p.getValueAsLong() : p.getValueAsString();
+
+			return invoker.invokeFindById(id).orElse(null);
 		}
 	}
 
@@ -785,23 +788,22 @@ public class PersistentEntityJackson2Module extends SimpleModule {
 				gen.writeStartArray();
 
 				for (Object element : (Collection<?>) value) {
-					gen.writeString(getLookupKey(element));
+					gen.writeObject(getLookupKey(element));
 				}
 
 				gen.writeEndArray();
 
 			} else {
-				gen.writeString(getLookupKey(value));
+				gen.writeObject(getLookupKey(value));
 			}
 		}
 
-		private String getLookupKey(Object value) {
+		private Object getLookupKey(Object value) {
 
-			Optional<EntityLookup<Object>> map = lookups.getPluginFor(value.getClass()).map(CastUtils::cast);
-
-			return map
+			return lookups.getPluginFor(value.getClass()) //
+					.<EntityLookup<Object>> map(CastUtils::cast)
 					.orElseThrow(() -> new IllegalArgumentException("No EntityLookup found for " + value.getClass().getName()))
-					.getResourceIdentifier(value).toString();
+					.getResourceIdentifier(value);
 		}
 	}
 }
diff --git a/spring-data-rest-webmvc/src/test/java/org/springframework/data/rest/webmvc/json/PersistentEntityJackson2ModuleUnitTests.java b/spring-data-rest-webmvc/src/test/java/org/springframework/data/rest/webmvc/json/PersistentEntityJackson2ModuleUnitTests.java
index 6bed9e66d..e448e6d38 100755
--- a/spring-data-rest-webmvc/src/test/java/org/springframework/data/rest/webmvc/json/PersistentEntityJackson2ModuleUnitTests.java
+++ b/spring-data-rest-webmvc/src/test/java/org/springframework/data/rest/webmvc/json/PersistentEntityJackson2ModuleUnitTests.java
@@ -16,12 +16,16 @@
 package org.springframework.data.rest.webmvc.json;
 
 import static org.assertj.core.api.Assertions.*;
+import static org.mockito.ArgumentMatchers.*;
 import static org.mockito.Mockito.*;
 
+import lombok.Getter;
+
 import java.io.IOException;
 import java.net.URI;
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.Optional;
 
 import org.junit.Before;
 import org.junit.Test;
@@ -32,9 +36,11 @@ import org.springframework.core.convert.TypeDescriptor;
 import org.springframework.data.keyvalue.core.mapping.context.KeyValueMappingContext;
 import org.springframework.data.mapping.PersistentProperty;
 import org.springframework.data.mapping.context.PersistentEntities;
+import org.springframework.data.repository.support.RepositoryInvoker;
 import org.springframework.data.repository.support.RepositoryInvokerFactory;
 import org.springframework.data.rest.core.UriToEntityConverter;
 import org.springframework.data.rest.core.mapping.ResourceMappings;
+import org.springframework.data.rest.core.support.EntityLookup;
 import org.springframework.data.rest.core.support.SelfLinkProvider;
 import org.springframework.data.rest.core.util.Java8PluginRegistry;
 import org.springframework.data.rest.webmvc.EmbeddedResourcesAssembler;
@@ -49,6 +55,8 @@ import org.springframework.hateoas.ResourceProcessor;
 import org.springframework.hateoas.UriTemplate;
 import org.springframework.hateoas.mvc.ResourceProcessorInvoker;
 
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonInclude.Include;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.annotation.JsonTypeInfo;
 import com.fasterxml.jackson.databind.ObjectMapper;
@@ -69,6 +77,7 @@ public class PersistentEntityJackson2ModuleUnitTests {
 	@Mock EntityLinks entityLinks;
 	@Mock ResourceMappings mappings;
 	@Mock SelfLinkProvider selfLinks;
+	@Mock RepositoryInvokerFactory factory;
 
 	PersistentEntities persistentEntities;
 	ObjectMapper mapper;
@@ -90,9 +99,9 @@ public class PersistentEntityJackson2ModuleUnitTests {
 		SimpleModule module = new SimpleModule();
 
 		module.setSerializerModifier(new AssociationOmittingSerializerModifier(persistentEntities, associations,
-				nestedEntitySerializer, new LookupObjectSerializer(Java8PluginRegistry.empty())));
-		module.setDeserializerModifier(new AssociationUriResolvingDeserializerModifier(persistentEntities, associations,
-				converter, mock(RepositoryInvokerFactory.class)));
+				nestedEntitySerializer, new LookupObjectSerializer(Java8PluginRegistry.of(Arrays.asList(new HomeLookup())))));
+		module.setDeserializerModifier(
+				new AssociationUriResolvingDeserializerModifier(persistentEntities, associations, converter, factory));
 
 		this.mapper = new ObjectMapper();
 		this.mapper.registerModule(module);
@@ -135,13 +144,71 @@ public class PersistentEntityJackson2ModuleUnitTests {
 		assertThat(petOwner.getPet()).isNotNull();
 	}
 
+	@Test // DATAREST-1321
+	public void allowsNumericIdsForLookupTypes() throws Exception {
+
+		RepositoryInvoker invoker = mock(RepositoryInvoker.class);
+		when(invoker.invokeFindById(any(Long.class))).thenReturn(Optional.of(new Home()));
+
+		when(factory.getInvokerFor(Home.class)).thenReturn(invoker);
+
+		PersistentProperty<?> property = persistentEntities.getRequiredPersistentEntity(PetOwner.class)
+				.getRequiredPersistentProperty("home");
+
+		when(associations.isLookupType(property)).thenReturn(true);
+
+		PetOwner petOwner = mapper.readValue("{\"home\": 1 }", PetOwner.class);
+
+		assertThat(petOwner).isNotNull();
+		assertThat(petOwner.getHome()).isInstanceOf(Home.class);
+	}
+
+	@Test // DATAREST-1321
+	public void serializesNonStringLookupValues() throws Exception {
+
+		// Given Pet defined as lookup type
+		PersistentProperty<?> property = persistentEntities.getRequiredPersistentEntity(PetOwner.class)
+				.getRequiredPersistentProperty("home");
+		when(associations.isLookupType(property)).thenReturn(true);
+
+		// When a Pet is rendered
+		PetOwner owner = new PetOwner();
+		owner.home = new Home();
+
+		String result = mapper.writeValueAsString(owner);
+
+		// The it appears as numeric value
+		assertThat(JsonPath.parse(result).read("$.home", Integer.class)) //
+				.isEqualTo(41);
+	}
+
+	/**
+	 * @author Oliver Gierke
+	 */
+	private static class HomeLookup implements EntityLookup<Home> {
+
+		@Override
+		public Object getResourceIdentifier(Home entity) {
+			return 41;
+		}
+
+		@Override
+		public boolean supports(Class<?> delimiter) {
+			return delimiter.equals(Home.class);
+		}
+
+		@Override
+		public Optional<Home> lookupEntity(Object id) {
+			return Optional.of(new Home());
+		}
+	}
+
+	@Getter
+	@JsonInclude(Include.NON_NULL)
 	static class PetOwner {
 
 		Pet pet;
-
-		public Pet getPet() {
-			return pet;
-		}
+		Home home;
 	}
 
 	@JsonTypeInfo(include = JsonTypeInfo.As.PROPERTY, use = JsonTypeInfo.Id.MINIMAL_CLASS)
@@ -149,6 +216,8 @@ public class PersistentEntityJackson2ModuleUnitTests {
 
 	static class Cat extends Pet {}
 
+	static class Home {}
+
 	static class Sample {
 		public @JsonProperty("foo") String name;
 	}