diff --git a/run.c b/run.c
index e5b12338..eb47fe5e 100644
--- a/run.c
+++ b/run.c
@@ -369,14 +369,24 @@ float* forward(Transformer* transformer, int token, int pos) {
 // ----------------------------------------------------------------------------
 // The Byte Pair Encoding (BPE) Tokenizer that translates strings <-> tokens
 
+typedef struct {
+    char *str;
+    int id;
+} TokenIndex;
+
 typedef struct {
     char** vocab;
     float* vocab_scores;
+    TokenIndex *sorted_vocab;
     int vocab_size;
     unsigned int max_token_length;
     char byte_piece[2];
 } Tokenizer;
 
+int compare_tokens(const void *a, const void *b) {
+    return strcmp(((TokenIndex*)a)->str, ((TokenIndex*)b)->str);
+}
+
 void build_tokenizer(Tokenizer* t, char* tokenizer_path, int vocab_size) {
     // i should have written the vocab_size into the tokenizer file... sigh
     t->vocab_size = vocab_size;
@@ -396,13 +406,31 @@ void build_tokenizer(Tokenizer* t, char* tokenizer_path, int vocab_size) {
         if (fread(t->vocab[i], len, 1, file) != 1) { fprintf(stderr, "failed read\n"); exit(EXIT_FAILURE); }
         t->vocab[i][len] = '\0'; // add the string terminating token
     }
+
+    t->sorted_vocab = NULL;
+
     fclose(file);
 }
 
+void sort_vocabulary(Tokenizer* t) 
+{
+    if (t->sorted_vocab == NULL) {
+        // sort vocabulary
+        t->sorted_vocab = malloc(t->vocab_size * sizeof(TokenIndex));
+        if (t->sorted_vocab == NULL) { fprintf(stderr, "failed malloc for sorted vocabulary\n"); exit(EXIT_FAILURE); }
+        for (int i = 0; i < t->vocab_size; i++) {
+            t->sorted_vocab[i].str = t->vocab[i];
+            t->sorted_vocab[i].id = i;
+        }
+        qsort(t->sorted_vocab, t->vocab_size, sizeof(TokenIndex), compare_tokens);
+    }
+}
+
 void free_tokenizer(Tokenizer* t) {
     for (int i = 0; i < t->vocab_size; i++) { free(t->vocab[i]); }
     free(t->vocab);
     free(t->vocab_scores);
+    free(t->sorted_vocab);
 }
 
 char* decode(Tokenizer* t, int prev_token, int token) {
@@ -422,15 +450,6 @@ char* decode(Tokenizer* t, int prev_token, int token) {
     return piece;
 }
 
-typedef struct {
-    char *str;
-    int id;
-} TokenIndex;
-
-int compare_tokens(const void *a, const void *b) {
-    return strcmp(((TokenIndex*)a)->str, ((TokenIndex*)b)->str);
-}
-
 int str_lookup(char *str, TokenIndex *sorted_vocab, int vocab_size) {
     // efficiently find the perfect match for str in vocab, return its index or -1 if not found
     TokenIndex tok = { .str = str }; // acts as the key to search for
@@ -441,20 +460,14 @@ int str_lookup(char *str, TokenIndex *sorted_vocab, int vocab_size) {
 void encode(Tokenizer* t, char *text, int *tokens, int *n_tokens) {
     // encode the string text (input) into an upper-bound preallocated tokens[] array
 
-    // sort vocabulary
-    TokenIndex *sorted_vocab = malloc(t->vocab_size * sizeof(TokenIndex));
-    for (int i = 0; i < t->vocab_size; i++) {
-        sorted_vocab[i].str = t->vocab[i];
-        sorted_vocab[i].id = i;
-    }
-    qsort(sorted_vocab, t->vocab_size, sizeof(TokenIndex), compare_tokens);
+    sort_vocabulary(t);
 
     // create a temporary buffer that will store merge candidates of always two consecutive tokens
     char* str_buffer = malloc((t->max_token_length*2 +1 +2) * sizeof(char)); // *2 for concat, +1 for null terminator +2 for UTF8 (in case max_token_lenght is 1)
     size_t str_len = 0;
 
     // add_dummy_prefix is true by default
-    tokens[0] = str_lookup(" ", sorted_vocab, t->vocab_size);
+    tokens[0] = str_lookup(" ", t->sorted_vocab, t->vocab_size);
     *n_tokens = 1; // the number of tokens
 
     // Okay UTF-8 time. This will get messy. Here is the reference from Wikipedia:
@@ -490,7 +503,7 @@ void encode(Tokenizer* t, char *text, int *tokens, int *n_tokens) {
         }
 
         // ok c+1 is not a continuation byte, so we've read in a full codepoint
-        int id = str_lookup(str_buffer, sorted_vocab, t->vocab_size);
+        int id = str_lookup(str_buffer, t->sorted_vocab, t->vocab_size);
 
         if (id != -1) {
             // we found this codepoint in vocab, add it as a token
@@ -515,7 +528,7 @@ void encode(Tokenizer* t, char *text, int *tokens, int *n_tokens) {
         for (int i=0; i < (*n_tokens-1); i++) {
             // check if we can merge the pair (tokens[i], tokens[i+1])
             sprintf(str_buffer, "%s%s", t->vocab[tokens[i]], t->vocab[tokens[i+1]]);
-            int id = str_lookup(str_buffer, sorted_vocab, t->vocab_size);
+            int id = str_lookup(str_buffer, t->sorted_vocab, t->vocab_size);
             if (id != -1 && t->vocab_scores[id] > best_score) {
                 // this merge pair exists in vocab! record its score and position
                 best_score = t->vocab_scores[id];
@@ -538,7 +551,6 @@ void encode(Tokenizer* t, char *text, int *tokens, int *n_tokens) {
     }
 
     free(str_buffer);
-    free(sorted_vocab);
 }
 
 // ----------------------------------------------------------------------------