diff --git a/examples/server/server.cpp b/examples/server/server.cpp
index 1f0e3a023..8d4c8229c 100644
--- a/examples/server/server.cpp
+++ b/examples/server/server.cpp
@@ -798,7 +798,7 @@ struct server_context {
         return last_used;
     }
 
-    bool launch_slot_with_data(server_slot & slot, json data) const {
+    bool launch_slot_with_data(server_slot & slot, json data, std::string & error_message) const {
         slot_params default_params;
         llama_sampling_params default_sparams;
 
@@ -841,12 +841,12 @@ struct server_context {
         }
 
         if (slot.n_predict > 0 && slot.params.n_predict > slot.n_predict) {
-            // Might be better to reject the request with a 400 ?
             LOG_WARNING("Max tokens to predict exceeds server configuration", {
                 {"params.n_predict", slot.params.n_predict},
                 {"slot.n_predict",   slot.n_predict},
             });
-            slot.params.n_predict = slot.n_predict;
+            error_message = "Max tokens to predict exceeds server configuration";
+            return false;
         }
 
         // infill
@@ -910,6 +910,7 @@ struct server_context {
             if (logit_bias != data.end() && logit_bias->is_array()) {
                 const int n_vocab = llama_n_vocab(model);
                 for (const auto & el : *logit_bias) {
+                    // TODO: we may want to throw errors here, in case "el" is incorrect
                     if (el.is_array() && el.size() == 2) {
                         float bias;
                         if (el[1].is_number()) {
@@ -969,6 +970,11 @@ struct server_context {
                 llama_sampling_free(slot.ctx_sampling);
             }
             slot.ctx_sampling = llama_sampling_init(slot.sparams);
+            if (slot.ctx_sampling == nullptr) {
+                // for now, the only error that may happen here is invalid grammar
+                error_message = "Failed to parse grammar";
+                return false;
+            }
             llama_set_rng_seed(ctx, slot.params.seed);
         }
 
@@ -1456,9 +1462,10 @@ struct server_context {
                     slot->infill    = task.infill;
                     slot->embedding = task.embedding;
 
-                    if (!launch_slot_with_data(*slot, task.data)) {
+                    std::string err_launch_slot;
+                    if (!launch_slot_with_data(*slot, task.data, err_launch_slot)) {
                         // send error result
-                        send_error(task, "Cannot launch slot");
+                        send_error(task, err_launch_slot.empty() ? "Cannot launch slot" : err_launch_slot);
                         break;
                     }
                 } break;