diff --git a/pagerduty/resource_pagerduty_incident_workflow_trigger.go b/pagerduty/resource_pagerduty_incident_workflow_trigger.go
index 0eaa50e98..891bbcd60 100644
--- a/pagerduty/resource_pagerduty_incident_workflow_trigger.go
+++ b/pagerduty/resource_pagerduty_incident_workflow_trigger.go
@@ -128,6 +128,11 @@ func resourcePagerDutyIncidentWorkflowTriggerDelete(ctx context.Context, d *sche
 }
 
 func validateIncidentWorkflowTrigger(_ context.Context, d *schema.ResourceDiff, _ interface{}) error {
+	oldType, newType := d.GetChange("type")
+	if oldType != nil && oldType != "" && oldType != newType {
+		return fmt.Errorf("trigger type cannot be changed")
+	}
+
 	triggerType := d.Get("type").(string)
 	_, hadCondition := d.GetOk("condition")
 	if triggerType == "manual" && hadCondition {
diff --git a/pagerduty/resource_pagerduty_incident_workflow_trigger_test.go b/pagerduty/resource_pagerduty_incident_workflow_trigger_test.go
index 3c2c444e8..ca64d5007 100644
--- a/pagerduty/resource_pagerduty_incident_workflow_trigger_test.go
+++ b/pagerduty/resource_pagerduty_incident_workflow_trigger_test.go
@@ -215,14 +215,8 @@ func TestAccPagerDutyIncidentWorkflowTrigger_BasicConditionalAllServices(t *test
 				),
 			},
 			{
-				Config: testAccCheckPagerDutyIncidentWorkflowTriggerConfigConditionalAllServices(workflow, "incident.priority matches 'P2'"),
-				Check: resource.ComposeTestCheckFunc(
-					testAccCheckPagerDutyIncidentWorkflowTriggerExists("pagerduty_incident_workflow_trigger.test"),
-					resource.TestCheckResourceAttr(
-						"pagerduty_incident_workflow_trigger.test", "type", "conditional"),
-					resource.TestCheckResourceAttr(
-						"pagerduty_incident_workflow_trigger.test", "condition", "incident.priority matches 'P2'"),
-				),
+				Config:      testAccCheckPagerDutyIncidentWorkflowTriggerConfigManualAllServices(workflow),
+				ExpectError: regexp.MustCompile("trigger type cannot be changed"),
 			},
 		},
 	})
@@ -242,6 +236,55 @@ resource "pagerduty_incident_workflow_trigger" "test" {
 `, testAccCheckPagerDutyIncidentWorkflowConfig(workflow), condition)
 }
 
+func testAccCheckPagerDutyIncidentWorkflowTriggerConfigManualAllServices(workflow string) string {
+	return fmt.Sprintf(`
+%s
+
+resource "pagerduty_incident_workflow_trigger" "test" {
+  type       = "manual"
+  workflow   = pagerduty_incident_workflow.test.id
+  services   = []
+  subscribed_to_all_services = true
+}
+`, testAccCheckPagerDutyIncidentWorkflowConfig(workflow))
+}
+
+func TestAccPagerDutyIncidentWorkflowTrigger_CannotChangeType(t *testing.T) {
+	workflow := fmt.Sprintf("tf-%s", acctest.RandString(5))
+
+	resource.Test(t, resource.TestCase{
+		PreCheck: func() {
+			testAccPreCheck(t)
+			testAccPreCheckIncidentWorkflows(t)
+		},
+		ProviderFactories: testAccProviderFactories,
+		CheckDestroy:      testAccCheckPagerDutyIncidentWorkflowTriggerDestroy,
+		Steps: []resource.TestStep{
+			{
+				Config: testAccCheckPagerDutyIncidentWorkflowTriggerConfigConditionalAllServices(workflow, "incident.priority matches 'P1'"),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckPagerDutyIncidentWorkflowTriggerExists("pagerduty_incident_workflow_trigger.test"),
+					resource.TestCheckResourceAttr(
+						"pagerduty_incident_workflow_trigger.test", "type", "conditional"),
+					resource.TestCheckResourceAttr(
+						"pagerduty_incident_workflow_trigger.test", "condition", "incident.priority matches 'P1'"),
+					resource.TestCheckResourceAttr("pagerduty_incident_workflow_trigger.test", "subscribed_to_all_services", "true"),
+				),
+			},
+			{
+				Config: testAccCheckPagerDutyIncidentWorkflowTriggerConfigConditionalAllServices(workflow, "incident.priority matches 'P2'"),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckPagerDutyIncidentWorkflowTriggerExists("pagerduty_incident_workflow_trigger.test"),
+					resource.TestCheckResourceAttr(
+						"pagerduty_incident_workflow_trigger.test", "type", "conditional"),
+					resource.TestCheckResourceAttr(
+						"pagerduty_incident_workflow_trigger.test", "condition", "incident.priority matches 'P2'"),
+				),
+			},
+		},
+	})
+}
+
 func testAccCheckPagerDutyIncidentWorkflowTriggerDestroy(s *terraform.State) error {
 	client, _ := testAccProvider.Meta().(*Config).Client()
 	for _, r := range s.RootModule().Resources {