diff --git a/issue.go b/issue.go
index ce30648..9d8bad1 100644
--- a/issue.go
+++ b/issue.go
@@ -588,11 +588,11 @@ func (s *IssueService) Create(issue *Issue) (*Issue, *Response, error) {
 	return responseIssue, resp, nil
 }
 
-// Update updates an issue from a JSON representation.
+// Update updates an issue from a JSON representation. The issue is found by key.
 //
 // JIRA API docs: https://docs.atlassian.com/jira/REST/cloud/#api/2/issue-editIssue
 func (s *IssueService) Update(issue *Issue) (*Issue, *Response, error) {
-	apiEndpoint := fmt.Sprintf("rest/api/2/issue/%v", issue.ID)
+	apiEndpoint := fmt.Sprintf("rest/api/2/issue/%v", issue.Key)
 	req, err := s.client.NewRequest("PUT", apiEndpoint, issue)
 	if err != nil {
 		return nil, nil, err
diff --git a/issue_test.go b/issue_test.go
index e2b54a9..940a38b 100644
--- a/issue_test.go
+++ b/issue_test.go
@@ -81,15 +81,15 @@ func TestIssueService_Create(t *testing.T) {
 func TestIssueService_Update(t *testing.T) {
 	setup()
 	defer teardown()
-	testMux.HandleFunc("/rest/api/2/issue/10002", func(w http.ResponseWriter, r *http.Request) {
+	testMux.HandleFunc("/rest/api/2/issue/PROJ-9001", func(w http.ResponseWriter, r *http.Request) {
 		testMethod(t, r, "PUT")
-		testRequestURL(t, r, "/rest/api/2/issue/10002")
+		testRequestURL(t, r, "/rest/api/2/issue/PROJ-9001")
 
 		w.WriteHeader(http.StatusNoContent)
 	})
 
 	i := &Issue{
-		ID: "10002",
+		Key: "PROJ-9001",
 		Fields: &IssueFields{
 			Description: "example bug report",
 		},