diff --git a/client_test.go b/client_test.go
index 7f9b24ed3..7bc0d596f 100644
--- a/client_test.go
+++ b/client_test.go
@@ -215,7 +215,7 @@ func TestRuntimeNotFound(t *testing.T) {
 	}
 }
 
-// TODO: TestRuntimeNotFoundCustom ensures that the correct error is returned
+// TestRuntimeNotFoundCustom ensures that the correct error is returned
 // when the requested runtime is not found in a given custom repository
 func TestRuntimeNotFoundCustom(t *testing.T) {
 	root := "testdata/example.com/testRuntimeNotFoundCustom"
@@ -224,7 +224,7 @@ func TestRuntimeNotFoundCustom(t *testing.T) {
 	}
 	defer os.RemoveAll(root)
 
-	// Create a new client with path to the extensible templates
+	// Create a new client with path to extensible templates
 	client := bosonFunc.New(
 		bosonFunc.WithTemplates("testdata/repositories"),
 		bosonFunc.WithRegistry(TestRegistry))
@@ -236,7 +236,7 @@ func TestRuntimeNotFoundCustom(t *testing.T) {
 	// creating should error as runtime not found
 	err := client.New(context.Background(), f)
 	if !errors.Is(err, bosonFunc.ErrRuntimeNotFound) {
-		t.Fatal(err)
+		t.Fatalf("Expected ErrRuntimeNotFound, got %v", err)
 	}
 }
 
@@ -250,16 +250,38 @@ func TestTemplateNotFound(t *testing.T) {
 
 	client := bosonFunc.New(bosonFunc.WithRegistry(TestRegistry))
 
-	// creating a Function with an unsupported runtime should bubble
-	// the error generated by the unsderlying template initializer.
+	// Creating a function with an invalid template shulid generate the
+	// appropriate error.
 	f := bosonFunc.Function{Root: root, Runtime: "go", Trigger: "invalid"}
 	err := client.New(context.Background(), f)
 	if !errors.Is(err, bosonFunc.ErrTemplateNotFound) {
-		t.Fatalf("Expected ErrRuntimeNotFound, got %T", err)
+		t.Fatalf("Expected ErrTemplateNotFound, got %v", err)
 	}
 }
 
-// TODO: TestTemplateNotFound in custom repository
+// TestTemplateNotFoundCustom ensures that the correct error is returned
+// when the requested template is not found in the given custom repository.
+func TestTemplateNotFoundCustom(t *testing.T) {
+	root := "testdata/example.com/testTemplateNotFoundCustom"
+	if err := os.MkdirAll(root, 0700); err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(root)
+
+	// Create a new client with path to extensible templates
+	client := bosonFunc.New(
+		bosonFunc.WithTemplates("testdata/repositories"),
+		bosonFunc.WithRegistry(TestRegistry))
+
+	// An invalid template, but a valid custom provider
+	f := bosonFunc.Function{Root: root, Runtime: "test", Trigger: "customProvider/invalid"}
+
+	// Creation should generate the correct error of template not being found.
+	err := client.New(context.Background(), f)
+	if !errors.Is(err, bosonFunc.ErrTemplateNotFound) {
+		t.Fatalf("Expected ErrTemplateNotFound, got %v", err)
+	}
+}
 
 // TestNamed ensures that an explicitly passed name is used in leau of the
 // path derived name when provided, and persists through instantiations.
diff --git a/templates.go b/templates.go
index d6b16cee2..d750c6b84 100644
--- a/templates.go
+++ b/templates.go
@@ -90,7 +90,7 @@ func isCustom(template string) bool {
 	return len(strings.Split(template, "/")) > 1
 }
 
-func (t *templateWriter) writeCustom(repositoriesPath, runtime, template, dest string) error {
+func (t *templateWriter) writeCustom(repositoriesPath, runtime, template, dest string) (err error) {
 	if repositoriesPath == "" {
 		return ErrRepositoriesNotDefined
 	}
@@ -104,11 +104,17 @@ func (t *templateWriter) writeCustom(repositoriesPath, runtime, template, dest s
 	repositoriesFS := os.DirFS(repositoriesPath)
 
 	runtimePath := cc[0] + "/" + runtime
-	_, err := fs.Stat(repositoriesFS, runtimePath)
+	_, err = fs.Stat(repositoriesFS, runtimePath)
 	if errors.Is(err, fs.ErrNotExist) {
 		return ErrRuntimeNotFound
 	}
 
+	templatePath := runtimePath + "/" + cc[1]
+	_, err = fs.Stat(repositoriesFS, templatePath)
+	if errors.Is(err, fs.ErrNotExist) {
+		return ErrTemplateNotFound
+	}
+
 	// ex: /home/alice/.config/func/repositories/boson/go/http
 	// Note that the FS instance returned by os.DirFS uses forward slashes
 	// internally, so source paths do not use the os path separator due to