diff --git a/examples/perplexity/perplexity.cpp b/examples/perplexity/perplexity.cpp
index c23eaefab..e32f86130 100644
--- a/examples/perplexity/perplexity.cpp
+++ b/examples/perplexity/perplexity.cpp
@@ -1074,6 +1074,48 @@ struct truthful_qa_task {
     std::vector<float> log_probs;
 };
 
+static bool truthful_qa_prepare_one_task(llama_context * ctx, bool add_bos, truthful_qa_task& task, bool log_error) {
+    if (task.question.empty() || task.mc1.answers.empty()) {
+        if (log_error) {
+            printf("%s: found bad task with empty question and/or answers\n", __func__);
+        }
+        return false;
+    }
+    task.seq_tokens.reserve(task.mc1.answers.size());
+    for (auto& answer : task.mc1.answers) {
+        if (answer.empty()) {
+            if (log_error) {
+                printf("%s: found empty answer\n", __func__);
+            }
+            return false;
+        }
+        task.seq_tokens.emplace_back(::llama_tokenize(ctx, task.question + " " + answer, add_bos));
+    }
+    auto min_len = task.seq_tokens.front().size();
+    for (auto& seq : task.seq_tokens) {
+        min_len = std::min(min_len, seq.size());
+    }
+    task.common_prefix = 0;
+    for (size_t k = 0; k < min_len; ++k) {
+        auto token = task.seq_tokens[0][k];
+        bool all_same = true;
+        for (size_t i = 1; i < task.seq_tokens.size(); ++i) {
+            if (task.seq_tokens[i][k] != token) {
+                all_same = false;
+                break;
+            }
+        }
+        if (!all_same) {
+            break;
+        }
+        ++task.common_prefix;
+    }
+    task.required_tokens = task.common_prefix;
+    for (auto& seq : task.seq_tokens) {
+        task.required_tokens += seq.size() - task.common_prefix;
+    }
+    return true;
+}
 
 static void truthful_qa_score(llama_context * ctx, const gpt_params & params) {
     // Calculates TruthFulQA score (multiple choice with single correct answer) from prompt
@@ -1141,51 +1183,55 @@ static void truthful_qa_score(llama_context * ctx, const gpt_params & params) {
 
     printf("%s: preparing task data", __func__);
     fflush(stdout);
-    int n_dot = n_task/100;
-    int i_task = 0;
-    for (auto& task : tasks) {
-        ++i_task;
-        if (task.question.empty() || task.mc1.answers.empty()) {
-            printf("%s: found bad task with empty question and/or answers\n", __func__);
-            return;
-        }
-        task.seq_tokens.reserve(task.mc1.answers.size());
-        for (auto& answer : task.mc1.answers) {
-            if (answer.empty()) {
-                printf("%s: found empty answer\n", __func__);
-                return;
-            }
-            task.seq_tokens.emplace_back(::llama_tokenize(ctx, task.question + " " + answer, add_bos));
-        }
-        auto min_len = task.seq_tokens.front().size();
-        for (auto& seq : task.seq_tokens) {
-            min_len = std::min(min_len, seq.size());
-        }
-        task.common_prefix = 0;
-        for (size_t k = 0; k < min_len; ++k) {
-            auto token = task.seq_tokens[0][k];
-            bool all_same = true;
-            for (size_t i = 1; i < task.seq_tokens.size(); ++i) {
-                if (task.seq_tokens[i][k] != token) {
-                    all_same = false;
+    if (n_task > 500) {
+        printf("...");
+        fflush(stdout);
+        constexpr int k_chunk = 4;
+        std::atomic<int> counter(0);
+        std::atomic<int> n_bad(0);
+        auto prepare = [&counter, &n_bad, &tasks, ctx, add_bos] () {
+            int num_tasks = tasks.size();
+            int n_bad_local = 0;
+            while (true) {
+                int first = counter.fetch_add(k_chunk);
+                if (first >= num_tasks) {
+                    if (n_bad_local > 0) n_bad += n_bad_local;
                     break;
                 }
+                int last = std::min(first + k_chunk, num_tasks);
+                for (int i = first; i < last; ++i) {
+                    if (!truthful_qa_prepare_one_task(ctx, add_bos, tasks[i], false)) ++n_bad_local;
+                }
             }
-            if (!all_same) {
-                break;
+        };
+        size_t max_thread = std::thread::hardware_concurrency();
+        max_thread = std::min(max_thread, (tasks.size() + k_chunk - 1)/k_chunk);
+        std::vector<std::thread> workers(max_thread-1);
+        for (auto& w : workers) w = std::thread(prepare);
+        prepare();
+        for (auto& w : workers) w.join();
+        printf("done\n");
+        fflush(stdout);
+        int nbad = n_bad;
+        if (nbad > 0) {
+            printf("%s: found %d malformed tasks\n", __func__, nbad);
+            return;
+        }
+    } else {
+        int n_dot = n_task/100;
+        int i_task = 0;
+        for (auto& task : tasks) {
+            ++i_task;
+            if (!truthful_qa_prepare_one_task(ctx, add_bos, task, true)) {
+                return;
+            }
+            if (i_task%n_dot == 0) {
+                printf(".");
+                fflush(stdout);
             }
-            ++task.common_prefix;
-        }
-        task.required_tokens = task.common_prefix;
-        for (auto& seq : task.seq_tokens) {
-            task.required_tokens += seq.size() - task.common_prefix;
-        }
-        if (i_task%n_dot == 0) {
-            printf(".");
-            fflush(stdout);
         }
+        printf("done\n");
     }
-    printf("done\n");
 
     printf("%s : calculating TruthfulQA score over %zu tasks.\n", __func__, tasks.size());