diff --git a/server/model.go b/server/model.go
index 4926d6ce2..644b47b04 100644
--- a/server/model.go
+++ b/server/model.go
@@ -302,7 +302,7 @@ func parseObjects(s string) []map[string]any {
 // mxyng: this only really works if the input contains tool calls in some JSON format
 func (m *Model) parseToolCalls(s string) ([]api.ToolCall, bool) {
 	// create a subtree from the node that ranges over .ToolCalls
-	tmpl := m.Template.Subtree(func(n parse.Node) bool {
+	tmpl := m.Template.Sub(func(n parse.Node) bool {
 		if t, ok := n.(*parse.RangeNode); ok {
 			return slices.Contains(template.Identifiers(t.Pipe), "ToolCalls")
 		}
@@ -315,7 +315,7 @@ func (m *Model) parseToolCalls(s string) ([]api.ToolCall, bool) {
 	}
 
 	var b bytes.Buffer
-	if err := tmpl.Execute(&b, map[string][]api.ToolCall{
+	if err := tmpl.Template().Execute(&b, map[string][]api.ToolCall{
 		"ToolCalls": {
 			{
 				Function: api.ToolCallFunction{
diff --git a/template/template.go b/template/template.go
index 5c886cac4..85be483ca 100644
--- a/template/template.go
+++ b/template/template.go
@@ -93,8 +93,8 @@ func Named(s string) (*named, error) {
 var DefaultTemplate, _ = Parse("{{ .Prompt }}")
 
 type Template struct {
-	*template.Template
-	raw string
+	tree *parse.Tree
+	raw  string
 }
 
 // response is a template node that can be added to templates that don't already have one
@@ -124,17 +124,18 @@ var funcs = template.FuncMap{
 }
 
 func Parse(s string) (*Template, error) {
-	tmpl := template.New("").Option("missingkey=zero").Funcs(funcs)
+	tree := parse.New("")
+	tree.Mode = tree.Mode | parse.SkipFuncCheck
 
-	tmpl, err := tmpl.Parse(s)
+	tree, err := tree.Parse(s, "", "", map[string]*parse.Tree{})
 	if err != nil {
 		return nil, err
 	}
 
-	t := Template{Template: tmpl, raw: s}
+	t := Template{tree, s}
 	if vars := t.Vars(); !slices.Contains(vars, "messages") && !slices.Contains(vars, "response") {
 		// touch up the template and append {{ .Response }}
-		tmpl.Tree.Root.Nodes = append(tmpl.Tree.Root.Nodes, &response)
+		t.tree.Root.Nodes = append(t.tree.Root.Nodes, &response)
 	}
 
 	return &t, nil
@@ -146,10 +147,8 @@ func (t *Template) String() string {
 
 func (t *Template) Vars() []string {
 	var vars []string
-	for _, tt := range t.Templates() {
-		for _, n := range tt.Root.Nodes {
-			vars = append(vars, Identifiers(n)...)
-		}
+	for _, n := range t.tree.Root.Nodes {
+		vars = append(vars, Identifiers(n)...)
 	}
 
 	set := make(map[string]struct{})
@@ -172,7 +171,8 @@ type Values struct {
 	forceLegacy bool
 }
 
-func (t *Template) Subtree(fn func(parse.Node) bool) *template.Template {
+// Sub returns a new template with the subtree that matches the predicate
+func (t *Template) Sub(fn func(parse.Node) bool) *Template {
 	var walk func(parse.Node) parse.Node
 	walk = func(n parse.Node) parse.Node {
 		if fn(n) {
@@ -205,29 +205,34 @@ func (t *Template) Subtree(fn func(parse.Node) bool) *template.Template {
 		return nil
 	}
 
-	if n := walk(t.Tree.Root); n != nil {
-		return (&template.Template{
-			Tree: &parse.Tree{
+	if n := walk(t.tree.Root); n != nil {
+		return &Template{
+			tree: &parse.Tree{
 				Root: &parse.ListNode{
 					Nodes: []parse.Node{n},
 				},
 			},
-		}).Funcs(funcs)
+		}
 	}
 
 	return nil
 }
 
+func (t *Template) Template() *template.Template {
+	return template.Must(template.New("").Option("missingkey=zero").Funcs(funcs).AddParseTree("", t.tree))
+}
+
 func (t *Template) Execute(w io.Writer, v Values) error {
+	tmpl := t.Template()
 	system, messages := collate(v.Messages)
 	if v.Prompt != "" && v.Suffix != "" {
-		return t.Template.Execute(w, map[string]any{
+		return tmpl.Execute(w, map[string]any{
 			"Prompt":   v.Prompt,
 			"Suffix":   v.Suffix,
 			"Response": "",
 		})
 	} else if !v.forceLegacy && slices.Contains(t.Vars(), "messages") {
-		return t.Template.Execute(w, map[string]any{
+		return tmpl.Execute(w, map[string]any{
 			"System":   system,
 			"Messages": messages,
 			"Tools":    v.Tools,
@@ -240,7 +245,7 @@ func (t *Template) Execute(w io.Writer, v Values) error {
 	var prompt, response string
 	for _, m := range messages {
 		execute := func() error {
-			if err := t.Template.Execute(&b, map[string]any{
+			if err := tmpl.Execute(&b, map[string]any{
 				"System":   system,
 				"Prompt":   prompt,
 				"Response": response,
@@ -275,7 +280,7 @@ func (t *Template) Execute(w io.Writer, v Values) error {
 	}
 
 	var cut bool
-	nodes := deleteNode(t.Template.Root.Copy(), func(n parse.Node) bool {
+	nodes := deleteNode(t.tree.Root.Copy(), func(n parse.Node) bool {
 		if field, ok := n.(*parse.FieldNode); ok && slices.Contains(field.Ident, "Response") {
 			cut = true
 			return false
@@ -285,7 +290,7 @@ func (t *Template) Execute(w io.Writer, v Values) error {
 	})
 
 	tree := parse.Tree{Root: nodes.(*parse.ListNode)}
-	if err := template.Must(template.New("").AddParseTree("", &tree)).Execute(&b, map[string]any{
+	if err := template.Must(tmpl.AddParseTree("", &tree)).Execute(&b, map[string]any{
 		"System":   system,
 		"Prompt":   prompt,
 		"Response": response,
diff --git a/template/template_test.go b/template/template_test.go
index 616bef6a8..ce13186cd 100644
--- a/template/template_test.go
+++ b/template/template_test.go
@@ -54,7 +54,7 @@ func TestNamed(t *testing.T) {
 					t.Fatal(err)
 				}
 
-				if tmpl.Tree.Root.String() == "" {
+				if tmpl.tree.Root.String() == "" {
 					t.Errorf("empty %s template", k)
 				}
 			})
@@ -153,7 +153,7 @@ func TestTemplate(t *testing.T) {
 	}
 }
 
-func TestParse(t *testing.T) {
+func TestParseVars(t *testing.T) {
 	cases := []struct {
 		template string
 		vars     []string
@@ -181,6 +181,9 @@ func TestParse(t *testing.T) {
 {{ end }}<|im_start|>assistant
 {{ .Response }}<|im_end|>
 {{- end -}}`, []string{"content", "messages", "prompt", "response", "role", "system"}},
+		{"{{ json .Messages }}", []string{"messages"}},
+		// undefined functions should not error
+		{"{{ undefined }}", []string{"response"}},
 	}
 
 	for _, tt := range cases {
@@ -197,6 +200,30 @@ func TestParse(t *testing.T) {
 	}
 }
 
+func TestParseExecute(t *testing.T) {
+	t.Run("undefined function", func(t *testing.T) {
+		tmpl, err := Parse(`{{- if .Suffix }}{{ .Prompt }} {{ .Suffix }}{{- else }}{{ undefined }}{{- end }}`)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		var b bytes.Buffer
+		if err := tmpl.Execute(&b, Values{Prompt: "def add(", Suffix: "    return c"}); err != nil {
+			t.Fatal(err)
+		}
+
+		if diff := cmp.Diff(b.String(), "def add(     return c"); diff != "" {
+			t.Errorf("mismatch (-got +want):\n%s", diff)
+		}
+
+		if err := tmpl.Execute(io.Discard, Values{}); err == nil {
+			t.Fatal("expected error")
+		} else if !strings.Contains(err.Error(), "\"undefined\" is not a defined function") {
+			t.Fatal(err)
+		}
+	})
+}
+
 func TestExecuteWithMessages(t *testing.T) {
 	type template struct {
 		name     string