diff --git a/benchmark/src/lib.rs b/benchmark/src/lib.rs
index e290665c..a0ef0fe6 100644
--- a/benchmark/src/lib.rs
+++ b/benchmark/src/lib.rs
@@ -45,7 +45,7 @@ pub async fn run(
         repetition_penalty: repetition_penalty.unwrap_or(1.0),
         frequency_penalty: frequency_penalty.unwrap_or(0.0),
         watermark,
-        fsm_grammar_state: Vec::new(),
+        fsm_grammar_state: 0,
     };
 
     // Initialize terminal properties
diff --git a/proto/generate.proto b/proto/generate.proto
index 015dd6e9..82081921 100644
--- a/proto/generate.proto
+++ b/proto/generate.proto
@@ -71,9 +71,9 @@ message NextTokenChooserParameters {
     /// token watermarking using "A Watermark for Large Language Models"
     bool watermark = 8;
     /// grammar (applied if not empty)
-    repeated string grammar = 10;
+    string grammar = 10;
     /// fsm_grammar_state
-    repeated uint32 fsm_grammar_state = 11;
+    uint32 fsm_grammar_state = 11;
 }
 
 message StoppingCriteriaParameters {
diff --git a/router/client/src/client.rs b/router/client/src/client.rs
index f26b6a69..38e6e0e3 100644
--- a/router/client/src/client.rs
+++ b/router/client/src/client.rs
@@ -128,8 +128,8 @@ impl Client {
                     repetition_penalty: 1.2,
                     frequency_penalty: 0.1,
                     watermark: true,
-                    grammar: Vec::new(),
-                    fsm_grammar_state: Vec::new(),
+                    grammar: String::new(),
+                    fsm_grammar_state: 0,
                 }),
                 stopping_parameters: Some(StoppingCriteriaParameters {
                     max_new_tokens: max_total_tokens - truncate,
diff --git a/router/src/health.rs b/router/src/health.rs
index 0605dca8..f3cac17e 100644
--- a/router/src/health.rs
+++ b/router/src/health.rs
@@ -45,8 +45,8 @@ impl Health {
                     repetition_penalty: 1.0,
                     frequency_penalty: 0.0,
                     watermark: false,
-                    grammar: Vec::new(),
-                    fsm_grammar_state: Vec::new(),
+                    grammar: String::new(),
+                    fsm_grammar_state: 0,
                 }),
                 stopping_parameters: Some(StoppingCriteriaParameters {
                     max_new_tokens: 1,
diff --git a/router/src/queue.rs b/router/src/queue.rs
index 21467aa7..0162b906 100644
--- a/router/src/queue.rs
+++ b/router/src/queue.rs
@@ -368,8 +368,8 @@ mod tests {
                     repetition_penalty: 0.0,
                     frequency_penalty: 0.0,
                     watermark: false,
-                    grammar: Vec::new(),
-                    fsm_grammar_state: Vec::new(),
+                    grammar: String::new(),
+                    fsm_grammar_state: 0,
                 },
                 stopping_parameters: StoppingCriteriaParameters {
                     ignore_eos_token: false,
diff --git a/router/src/validation.rs b/router/src/validation.rs
index 83a68435..2959459d 100644
--- a/router/src/validation.rs
+++ b/router/src/validation.rs
@@ -294,9 +294,9 @@ impl Validation {
             .await?;
 
         // initialize the grammar parameter
-        let grammar = vec![grammar];
+        let grammar = grammar;
         // init the start state of the grammar
-        let fsm_grammar_state = vec![0];
+        let fsm_grammar_state = 0;
 
         let parameters = NextTokenChooserParameters {
             temperature,