diff --git a/rcl_action/src/rcl_action/action_server.c b/rcl_action/src/rcl_action/action_server.c
index 271d195..9d17d17 100644
--- a/rcl_action/src/rcl_action/action_server.c
+++ b/rcl_action/src/rcl_action/action_server.c
@@ -746,6 +746,8 @@ rcl_action_process_cancel_request(
   if (!uuidcmpzero(request_uuid) && (0u == request_nanosec)) {
     // UUID is not zero and timestamp is zero; cancel exactly one goal (if it exists)
     rcl_action_goal_info_t goal_info = rcl_action_get_zero_initialized_goal_info();
+    // Assume the goal ID is invalid until we find it
+    cancel_response->msg.return_code = action_msgs__srv__CancelGoal_Response__ERROR_UNKNOWN_GOAL_ID;
     rcl_action_goal_handle_t * goal_handle;
     for (size_t i = 0u; i < total_num_goals; ++i) {
       goal_handle = action_server->impl->goal_handles[i];
@@ -758,11 +760,18 @@ rcl_action_process_cancel_request(
       if (uuidcmp(request_uuid, goal_info.goal_id.uuid)) {
         if (rcl_action_goal_handle_is_cancelable(goal_handle)) {
           goal_handles_to_cancel[num_goals_to_cancel++] = goal_handle;
+          cancel_response->msg.return_code = action_msgs__srv__CancelGoal_Response__ERROR_NONE;
+        } else {
+          // If the goal is not cancelable, it must be because it is in a terminal state
+          cancel_response->msg.return_code =
+            action_msgs__srv__CancelGoal_Response__ERROR_GOAL_TERMINATED;
         }
         break;
       }
     }
   } else {
+    // The caller can later update the response code to reject the request if desired
+    cancel_response->msg.return_code = action_msgs__srv__CancelGoal_Response__ERROR_NONE;
     if (uuidcmpzero(request_uuid) && (0u == request_nanosec)) {
       // UUID and timestamp are both zero; cancel all goals
       // Set timestamp to max to cancel all active goals in the following for-loop
diff --git a/rcl_action/src/rcl_action/types.c b/rcl_action/src/rcl_action/types.c
index c072845..4e6ce33 100644
--- a/rcl_action/src/rcl_action/types.c
+++ b/rcl_action/src/rcl_action/types.c
@@ -44,7 +44,7 @@ rcl_action_get_zero_initialized_cancel_request(void)
 rcl_action_cancel_response_t
 rcl_action_get_zero_initialized_cancel_response(void)
 {
-  static rcl_action_cancel_response_t response = {{{0, 0, 0}}, {0, 0, 0, 0, 0}};
+  static rcl_action_cancel_response_t response = {{0, {0, 0, 0}}, {0, 0, 0, 0, 0}};
   return response;
 }
 
@@ -104,7 +104,7 @@ rcl_action_cancel_response_init(
     return RCL_RET_INVALID_ARGUMENT;
   }
   // Ensure cancel response is zero initialized
-  if (cancel_response->msg.goals_canceling.size > 0) {
+  if (0 != cancel_response->msg.return_code || cancel_response->msg.goals_canceling.size > 0) {
     RCL_SET_ERROR_MSG("cancel_response already inititalized");
     return RCL_RET_ALREADY_INIT;
   }
diff --git a/rcl_action/test/rcl_action/test_action_server.cpp b/rcl_action/test/rcl_action/test_action_server.cpp
index 0bd6c54..aa6fe75 100644
--- a/rcl_action/test/rcl_action/test_action_server.cpp
+++ b/rcl_action/test/rcl_action/test_action_server.cpp
@@ -17,6 +17,8 @@
 #include <thread>
 #include <vector>
 
+#include "action_msgs/srv/cancel_goal.h"
+
 #include "rcl_action/action_server.h"
 
 #include "rcl/error_handling.h"
@@ -376,6 +378,8 @@ TEST_F(TestActionServer, test_action_process_cancel_request)
   EXPECT_EQ(ret, RCL_RET_OK) << rcl_get_error_string().str;
   EXPECT_EQ(cancel_response.msg.goals_canceling.data, nullptr);
   EXPECT_EQ(cancel_response.msg.goals_canceling.size, 0u);
+  // A zero request means "cancel all goals", which succeeds if there's nothing to cancel
+  EXPECT_EQ(cancel_response.msg.return_code, action_msgs__srv__CancelGoal_Response__ERROR_NONE);
 }
 
 TEST_F(TestActionServer, test_action_server_get_goal_status_array)
@@ -537,6 +541,7 @@ TEST_F(TestActionServerCancelPolicy, test_action_process_cancel_request_all_goal
   EXPECT_EQ(ret, RCL_RET_OK) << rcl_get_error_string().str;
   EXPECT_NE(cancel_response.msg.goals_canceling.data, nullptr);
   ASSERT_EQ(cancel_response.msg.goals_canceling.size, (size_t)NUM_GOALS);
+  EXPECT_EQ(cancel_response.msg.return_code, action_msgs__srv__CancelGoal_Response__ERROR_NONE);
   rcl_action_goal_info_t * goal_info_out;
   for (int i = 0; i < NUM_GOALS; ++i) {
     goal_info_out = &cancel_response.msg.goals_canceling.data[i];
@@ -549,18 +554,60 @@ TEST_F(TestActionServerCancelPolicy, test_action_process_cancel_request_all_goal
 
 TEST_F(TestActionServerCancelPolicy, test_action_process_cancel_request_single_goal)
 {
-  // Request to cancel a specific goal
-  rcl_action_cancel_request_t cancel_request = rcl_action_get_zero_initialized_cancel_request();
-  init_test_uuid0(cancel_request.goal_info.goal_id.uuid);
-  rcl_action_cancel_response_t cancel_response = rcl_action_get_zero_initialized_cancel_response();
-  rcl_ret_t ret = rcl_action_process_cancel_request(
-    &this->action_server, &cancel_request, &cancel_response);
-  EXPECT_EQ(ret, RCL_RET_OK) << rcl_get_error_string().str;
-  EXPECT_NE(cancel_response.msg.goals_canceling.data, nullptr);
-  ASSERT_EQ(cancel_response.msg.goals_canceling.size, 1u);
-  rcl_action_goal_info_t * goal_info = &cancel_response.msg.goals_canceling.data[0];
-  EXPECT_TRUE(uuidcmp(goal_info->goal_id.uuid, cancel_request.goal_info.goal_id.uuid));
-  EXPECT_EQ(RCL_RET_OK, rcl_action_cancel_response_fini(&cancel_response));
+  {
+    // Request to cancel a specific goal
+    rcl_action_cancel_request_t cancel_request = rcl_action_get_zero_initialized_cancel_request();
+    init_test_uuid0(cancel_request.goal_info.goal_id.uuid);
+    rcl_action_cancel_response_t cancel_response =
+      rcl_action_get_zero_initialized_cancel_response();
+    rcl_ret_t ret = rcl_action_process_cancel_request(
+      &this->action_server, &cancel_request, &cancel_response);
+    EXPECT_EQ(ret, RCL_RET_OK) << rcl_get_error_string().str;
+    EXPECT_NE(cancel_response.msg.goals_canceling.data, nullptr);
+    ASSERT_EQ(cancel_response.msg.goals_canceling.size, 1u);
+    EXPECT_EQ(cancel_response.msg.return_code, action_msgs__srv__CancelGoal_Response__ERROR_NONE);
+    rcl_action_goal_info_t * goal_info = &cancel_response.msg.goals_canceling.data[0];
+    EXPECT_TRUE(uuidcmp(goal_info->goal_id.uuid, cancel_request.goal_info.goal_id.uuid));
+    EXPECT_EQ(RCL_RET_OK, rcl_action_cancel_response_fini(&cancel_response));
+  }
+  {
+    // Request to cancel an invalid goal
+    rcl_action_cancel_request_t cancel_request = rcl_action_get_zero_initialized_cancel_request();
+    init_test_uuid1(cancel_request.goal_info.goal_id.uuid);
+    rcl_action_cancel_response_t cancel_response =
+      rcl_action_get_zero_initialized_cancel_response();
+    rcl_ret_t ret = rcl_action_process_cancel_request(
+      &this->action_server, &cancel_request, &cancel_response);
+    EXPECT_EQ(ret, RCL_RET_OK) << rcl_get_error_string().str;
+    EXPECT_EQ(cancel_response.msg.goals_canceling.data, nullptr);
+    EXPECT_EQ(cancel_response.msg.goals_canceling.size, 0u);
+    EXPECT_EQ(
+      cancel_response.msg.return_code,
+      action_msgs__srv__CancelGoal_Response__ERROR_UNKNOWN_GOAL_ID);
+    EXPECT_EQ(RCL_RET_OK, rcl_action_cancel_response_fini(&cancel_response));
+  }
+  {
+    // Request to cancel a terminated goal
+    // First, transition a goal handle to a terminal state
+    rcl_ret_t ret = rcl_action_update_goal_state(&this->handles[3], GOAL_EVENT_EXECUTE);
+    ASSERT_EQ(RCL_RET_OK, ret) << rcl_get_error_string().str;
+    ret = rcl_action_update_goal_state(&this->handles[3], GOAL_EVENT_SUCCEED);
+    ASSERT_EQ(RCL_RET_OK, ret) << rcl_get_error_string().str;
+    // Attempt to cancel the terminated goal
+    rcl_action_cancel_request_t cancel_request = rcl_action_get_zero_initialized_cancel_request();
+    cancel_request.goal_info.goal_id = this->goal_infos_out[3].goal_id;
+    rcl_action_cancel_response_t cancel_response =
+      rcl_action_get_zero_initialized_cancel_response();
+    ret = rcl_action_process_cancel_request(
+      &this->action_server, &cancel_request, &cancel_response);
+    EXPECT_EQ(ret, RCL_RET_OK) << rcl_get_error_string().str;
+    EXPECT_EQ(cancel_response.msg.goals_canceling.data, nullptr);
+    EXPECT_EQ(cancel_response.msg.goals_canceling.size, 0u);
+    EXPECT_EQ(
+      cancel_response.msg.return_code,
+      action_msgs__srv__CancelGoal_Response__ERROR_GOAL_TERMINATED);
+    EXPECT_EQ(RCL_RET_OK, rcl_action_cancel_response_fini(&cancel_response));
+  }
 }
 
 TEST_F(TestActionServerCancelPolicy, test_action_process_cancel_request_by_time)
@@ -575,6 +622,7 @@ TEST_F(TestActionServerCancelPolicy, test_action_process_cancel_request_by_time)
   EXPECT_EQ(ret, RCL_RET_OK) << rcl_get_error_string().str;
   EXPECT_NE(cancel_response.msg.goals_canceling.data, nullptr);
   ASSERT_EQ(cancel_response.msg.goals_canceling.size, time_index + 1);  // goals at indices [0, 7]
+  EXPECT_EQ(cancel_response.msg.return_code, action_msgs__srv__CancelGoal_Response__ERROR_NONE);
   rcl_action_goal_info_t * goal_info_out;
   for (size_t i = 0; i < cancel_response.msg.goals_canceling.size; ++i) {
     goal_info_out = &cancel_response.msg.goals_canceling.data[i];
@@ -600,6 +648,7 @@ TEST_F(TestActionServerCancelPolicy, test_action_process_cancel_request_by_time_
     &this->action_server, &cancel_request, &cancel_response);
   EXPECT_EQ(ret, RCL_RET_OK) << rcl_get_error_string().str;
   EXPECT_NE(cancel_response.msg.goals_canceling.data, nullptr);
+  EXPECT_EQ(cancel_response.msg.return_code, action_msgs__srv__CancelGoal_Response__ERROR_NONE);
   const size_t num_goals_canceling = cancel_response.msg.goals_canceling.size;
   ASSERT_EQ(num_goals_canceling, time_index + 2);  // goals at indices [0, 2] and 8
   rcl_action_goal_info_t * goal_info_out;
diff --git a/rcl_action/test/rcl_action/test_types.cpp b/rcl_action/test/rcl_action/test_types.cpp
index f9f24d0..b31c110 100644
--- a/rcl_action/test/rcl_action/test_types.cpp
+++ b/rcl_action/test/rcl_action/test_types.cpp
@@ -67,6 +67,7 @@ TEST(TestActionTypes, test_get_zero_initialized_cancel_response)
   rcl_action_cancel_response_t cancel_response = rcl_action_get_zero_initialized_cancel_response();
   EXPECT_EQ(cancel_response.msg.goals_canceling.size, 0u);
   EXPECT_EQ(cancel_response.msg.goals_canceling.data, nullptr);
+  EXPECT_EQ(cancel_response.msg.return_code, 0);
 }
 
 TEST(TestActionTypes, test_init_fini_goal_status_array)
@@ -133,6 +134,7 @@ TEST(TestActionTypes, test_init_fini_cancel_response)
   EXPECT_EQ(ret, RCL_RET_INVALID_ARGUMENT);
   EXPECT_EQ(cancel_response.msg.goals_canceling.size, 0u);
   EXPECT_EQ(cancel_response.msg.goals_canceling.data, nullptr);
+  EXPECT_EQ(cancel_response.msg.return_code, 0);
 
   // Initialize with zero size
   cancel_response = rcl_action_get_zero_initialized_cancel_response();
@@ -141,6 +143,7 @@ TEST(TestActionTypes, test_init_fini_cancel_response)
   EXPECT_EQ(ret, RCL_RET_INVALID_ARGUMENT);
   EXPECT_EQ(cancel_response.msg.goals_canceling.size, 0u);
   EXPECT_EQ(cancel_response.msg.goals_canceling.data, nullptr);
+  EXPECT_EQ(cancel_response.msg.return_code, 0);
 
   // Initialize with valid arguments
   cancel_response = rcl_action_get_zero_initialized_cancel_response();
@@ -152,6 +155,7 @@ TEST(TestActionTypes, test_init_fini_cancel_response)
   EXPECT_EQ(ret, RCL_RET_OK);
   EXPECT_EQ(cancel_response.msg.goals_canceling.size, num_goals_canceling);
   EXPECT_NE(cancel_response.msg.goals_canceling.data, nullptr);
+  EXPECT_EQ(cancel_response.msg.return_code, action_msgs__srv__CancelGoal_Response__ERROR_NONE);
 
   // Finalize with invalid cancel response
   ret = rcl_action_cancel_response_fini(nullptr);