diff --git a/spring-cloud-open-service-broker-autoconfigure/src/test/java/org/springframework/cloud/servicebroker/autoconfigure/web/AbstractServiceInstanceControllerIntegrationTest.java b/spring-cloud-open-service-broker-autoconfigure/src/test/java/org/springframework/cloud/servicebroker/autoconfigure/web/AbstractServiceInstanceControllerIntegrationTest.java
index 426b38ed..548b0ac6 100644
--- a/spring-cloud-open-service-broker-autoconfigure/src/test/java/org/springframework/cloud/servicebroker/autoconfigure/web/AbstractServiceInstanceControllerIntegrationTest.java
+++ b/spring-cloud-open-service-broker-autoconfigure/src/test/java/org/springframework/cloud/servicebroker/autoconfigure/web/AbstractServiceInstanceControllerIntegrationTest.java
@@ -125,6 +125,11 @@ protected void setupServiceInstanceService(ServiceInstanceDoesNotExistException
 				.willReturn(Mono.error(exception));
 	}
 
+	protected void setupServiceInstanceServiceLastOperation(ServiceInstanceDoesNotExistException exception) {
+		given(serviceInstanceService.getLastOperation(any(GetLastServiceOperationRequest.class)))
+				.willReturn(Mono.error(exception));
+	}
+
 	protected void setupServiceInstanceService(UpdateServiceInstanceResponse response) {
 		given(serviceInstanceService.updateServiceInstance(any(UpdateServiceInstanceRequest.class)))
 				.willReturn(Mono.just(response));
diff --git a/spring-cloud-open-service-broker-autoconfigure/src/test/java/org/springframework/cloud/servicebroker/autoconfigure/web/reactive/ServiceInstanceControllerIntegrationTest.java b/spring-cloud-open-service-broker-autoconfigure/src/test/java/org/springframework/cloud/servicebroker/autoconfigure/web/reactive/ServiceInstanceControllerIntegrationTest.java
index b5445a43..853f10a4 100644
--- a/spring-cloud-open-service-broker-autoconfigure/src/test/java/org/springframework/cloud/servicebroker/autoconfigure/web/reactive/ServiceInstanceControllerIntegrationTest.java
+++ b/spring-cloud-open-service-broker-autoconfigure/src/test/java/org/springframework/cloud/servicebroker/autoconfigure/web/reactive/ServiceInstanceControllerIntegrationTest.java
@@ -53,6 +53,7 @@
 import org.springframework.test.web.reactive.server.WebTestClient;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.hamcrest.core.StringContains.containsString;
 import static org.springframework.cloud.servicebroker.exception.ServiceBrokerAsyncRequiredException.ASYNC_REQUIRED_ERROR;
 import static org.springframework.cloud.servicebroker.exception.ServiceBrokerMaintenanceInfoConflictException.MAINTENANCE_INFO_CONFLICT_ERROR;
 import static org.springframework.cloud.servicebroker.exception.ServiceBrokerMaintenanceInfoConflictException.MAINTENANCE_INFO_CONFLICT_MESSAGE;
@@ -787,6 +788,20 @@ void lastOperationHasSucceededStatusWithDeletionComplete() {
 				.jsonPath("$.description").isEqualTo("all gone");
 	}
 
+	@Test
+	void lastOperationWithUnknownInstanceBadRequest() {
+		setupServiceInstanceServiceLastOperation(new ServiceInstanceDoesNotExistException("nonexistent-instance-id"));
+
+		client.get().uri(buildLastOperationUrl())
+				.accept(MediaType.APPLICATION_JSON)
+				.exchange()
+				.expectStatus().is4xxClientError()
+				.expectStatus().isEqualTo(HttpStatus.BAD_REQUEST)
+				.expectBody()
+				.jsonPath("$.state").doesNotExist()
+				.jsonPath("$.description").value(containsString("The requested Service Instance does not exist"));
+	}
+
 	@Test
 	void lastOperationHasFailedStatus() {
 		setupServiceInstanceService(GetLastServiceOperationResponse.builder()
diff --git a/spring-cloud-open-service-broker-autoconfigure/src/test/java/org/springframework/cloud/servicebroker/autoconfigure/web/servlet/ServiceInstanceControllerIntegrationTest.java b/spring-cloud-open-service-broker-autoconfigure/src/test/java/org/springframework/cloud/servicebroker/autoconfigure/web/servlet/ServiceInstanceControllerIntegrationTest.java
index c619e65a..e38e5bf7 100644
--- a/spring-cloud-open-service-broker-autoconfigure/src/test/java/org/springframework/cloud/servicebroker/autoconfigure/web/servlet/ServiceInstanceControllerIntegrationTest.java
+++ b/spring-cloud-open-service-broker-autoconfigure/src/test/java/org/springframework/cloud/servicebroker/autoconfigure/web/servlet/ServiceInstanceControllerIntegrationTest.java
@@ -861,6 +861,21 @@ void lastOperationHasSucceededStatusWithDeletionComplete() throws Exception {
 				.andExpect(jsonPath("$.description", is("all gone")));
 	}
 
+	@Test
+	void lastOperationWithUnknownInstanceBadRequest() throws Exception {
+		setupServiceInstanceServiceLastOperation(new ServiceInstanceDoesNotExistException("nonexistent-instance-id"));
+
+		MvcResult mvcResult = mockMvc.perform(get(buildLastOperationUrl()))
+				.andExpect(request().asyncStarted())
+				.andReturn();
+
+		mockMvc.perform(asyncDispatch(mvcResult))
+				.andExpect(status().isBadRequest())
+				.andExpect(jsonPath("$.state").doesNotExist())
+				.andExpect(jsonPath("$.description",
+						containsString("The requested Service Instance does not exist")));
+	}
+
 	@Test
 	void lastOperationHasFailedStatus() throws Exception {
 		setupServiceInstanceService(GetLastServiceOperationResponse.builder()
diff --git a/spring-cloud-open-service-broker-core/src/main/java/org/springframework/cloud/servicebroker/controller/ServiceInstanceController.java b/spring-cloud-open-service-broker-core/src/main/java/org/springframework/cloud/servicebroker/controller/ServiceInstanceController.java
index 53e32d33..a77143bd 100644
--- a/spring-cloud-open-service-broker-core/src/main/java/org/springframework/cloud/servicebroker/controller/ServiceInstanceController.java
+++ b/spring-cloud-open-service-broker-core/src/main/java/org/springframework/cloud/servicebroker/controller/ServiceInstanceController.java
@@ -241,9 +241,20 @@ public Mono<ResponseEntity<GetLastServiceOperationResponse>> getServiceInstanceL
 						.doOnError(e -> LOG.error("Error getting service instance last operation. error=" +
 								e.getMessage(), e)))
 				.map(response -> {
-					boolean isSuccessfulDelete = response.getState().equals(OperationState.SUCCEEDED) && response
+					boolean isSuccessfulDelete = OperationState.SUCCEEDED.equals(response.getState()) && response
 							.isDeleteOperation();
 					return new ResponseEntity<>(response, isSuccessfulDelete ? HttpStatus.GONE : HttpStatus.OK);
+				})
+				.onErrorResume(e -> {
+					if (e instanceof ServiceInstanceDoesNotExistException) {
+						// TODO: v2.16 of the OSB API spec changes this to an HTTP 404
+						return Mono.just(new ResponseEntity<>(GetLastServiceOperationResponse.builder()
+								.description("The requested Service Instance does not exist")
+								.build(), HttpStatus.BAD_REQUEST));
+					}
+					else {
+						return Mono.error(e);
+					}
 				});
 	}
 
diff --git a/spring-cloud-open-service-broker-core/src/test/java/org/springframework/cloud/servicebroker/controller/ServiceInstanceControllerResponseCodeTest.java b/spring-cloud-open-service-broker-core/src/test/java/org/springframework/cloud/servicebroker/controller/ServiceInstanceControllerResponseCodeTest.java
index 5de184b3..be591450 100755
--- a/spring-cloud-open-service-broker-core/src/test/java/org/springframework/cloud/servicebroker/controller/ServiceInstanceControllerResponseCodeTest.java
+++ b/spring-cloud-open-service-broker-core/src/test/java/org/springframework/cloud/servicebroker/controller/ServiceInstanceControllerResponseCodeTest.java
@@ -313,6 +313,20 @@ void getLastOperationWithDeleteSucceededResponseGivesExpectedStatus() {
 				.build(), HttpStatus.GONE);
 	}
 
+	@Test
+	void getLastOperationWithUnknownInstanceBadRequest() {
+		given(serviceInstanceService.getLastOperation(any(GetLastServiceOperationRequest.class)))
+				.willReturn(Mono.error(new ServiceInstanceDoesNotExistException("instance never existed")));
+
+		ResponseEntity<GetLastServiceOperationResponse> responseEntity = controller
+				.getServiceInstanceLastOperation(pathVariables, null, "service-definition-id",
+						"service-definition-plan-id", null, null, null, null)
+				.block();
+
+		assertThat(responseEntity).isNotNull();
+		assertThat(responseEntity.getStatusCode()).isEqualTo(HttpStatus.BAD_REQUEST);
+	}
+
 	@Test
 	void getLastOperationWithFailedResponseGivesExpectedStatus() {
 		validateGetLastOperationWithResponseStatus(GetLastServiceOperationResponse.builder()