diff --git a/cmd/gh-aw/main_entry_test.go b/cmd/gh-aw/main_entry_test.go
index e5b9fee45f8..dc075cdcf12 100644
--- a/cmd/gh-aw/main_entry_test.go
+++ b/cmd/gh-aw/main_entry_test.go
@@ -33,6 +33,11 @@ func TestValidateEngine(t *testing.T) {
 			engine:    "codex",
 			expectErr: false,
 		},
+		{
+			name:      "valid copilot engine",
+			engine:    "copilot",
+			expectErr: false,
+		},
 		{
 			name:       "invalid engine",
 			engine:     "gpt4",
@@ -75,7 +80,7 @@ func TestValidateEngine(t *testing.T) {
 					return
 				}
 
-				if tt.errMessage != "" && err.Error() != fmt.Sprintf("invalid engine value '%s'. Must be 'claude' or 'codex'", tt.engine) {
+				if tt.errMessage != "" && err.Error() != fmt.Sprintf("invalid engine value '%s'. Must be 'copilot', 'claude' or 'codex'", tt.engine) {
 					t.Errorf("validateEngine(%q) error message = %v, want to contain %v", tt.engine, err.Error(), tt.errMessage)
 				}
 			} else {
diff --git a/pkg/parser/schema_test.go b/pkg/parser/schema_test.go
index d6b6a5230ea..54339467cbd 100644
--- a/pkg/parser/schema_test.go
+++ b/pkg/parser/schema_test.go
@@ -116,7 +116,7 @@ func TestValidateMainWorkflowFrontmatterWithSchema(t *testing.T) {
 				"engine": "invalid-engine",
 			},
 			wantErr:     true,
-			errContains: "value must be one of 'claude', 'codex'",
+			errContains: "value must be one of 'copilot', 'claude', 'codex', 'custom'",
 		},
 		{
 			name: "invalid engine object format - invalid id",
@@ -127,7 +127,7 @@ func TestValidateMainWorkflowFrontmatterWithSchema(t *testing.T) {
 				},
 			},
 			wantErr:     true,
-			errContains: "value must be one of 'claude', 'codex'",
+			errContains: "value must be one of 'claude', 'codex', 'custom'",
 		},
 		{
 			name: "invalid engine object format - missing id",
diff --git a/pkg/workflow/agentic_engine_test.go b/pkg/workflow/agentic_engine_test.go
index 4ec48c7e333..b754a8196a6 100644
--- a/pkg/workflow/agentic_engine_test.go
+++ b/pkg/workflow/agentic_engine_test.go
@@ -9,8 +9,8 @@ func TestEngineRegistry(t *testing.T) {
 
 	// Test that built-in engines are registered
 	supportedEngines := registry.GetSupportedEngines()
-	if len(supportedEngines) != 3 {
-		t.Errorf("Expected 3 supported engines, got %d", len(supportedEngines))
+	if len(supportedEngines) != 4 {
+		t.Errorf("Expected 4 supported engines, got %d", len(supportedEngines))
 	}
 
 	// Test getting engines by ID
@@ -116,7 +116,7 @@ func TestEngineRegistryCustomEngine(t *testing.T) {
 
 	// Test that supported engines list is updated
 	supportedEngines := registry.GetSupportedEngines()
-	if len(supportedEngines) != 4 {
-		t.Errorf("Expected 4 supported engines after adding test-custom, got %d", len(supportedEngines))
+	if len(supportedEngines) != 5 {
+		t.Errorf("Expected 5 supported engines after adding test-custom, got %d", len(supportedEngines))
 	}
 }