diff --git a/sample/samplers.go b/sample/samplers.go
index 8c0690f9d..12c3dafd8 100644
--- a/sample/samplers.go
+++ b/sample/samplers.go
@@ -171,6 +171,9 @@ type Grammar struct {
 
 func NewGrammar(vocab *model.Vocabulary, grammarStr string) (*Grammar, error) {
 	grammar := llama.InitGrammarChain(grammarStr)
+	if grammar == nil {
+		return nil, errors.New("sample: failed to initialize grammar")
+	}
 	for _, s := range vocab.Values {
 		id := vocab.Encode(s)
 		grammar.AddSymbol(s, uint32(id))