diff --git a/src/builder.rs b/src/builder.rs
index 7e865a8..43a6fd4 100644
--- a/src/builder.rs
+++ b/src/builder.rs
@@ -103,7 +103,7 @@ impl SymbolTable {
     fn optimize(&self, counters: Counter) -> Self {
         let mut res = SymbolTable::default();
         let mut pqueue = BinaryHeap::new();
-        for code1 in 0..511 {
+        for code1 in 0u16..(256u16 + self.n_symbols as u16) {
             let symbol1 = self.symbols[code1 as usize];
             let gain = counters.count1(code1) * symbol1.len();
             pqueue.push(Candidate {
@@ -111,7 +111,7 @@ impl SymbolTable {
                 gain,
             });
 
-            for code2 in 0..511 {
+            for code2 in 0u16..(256u16 + self.n_symbols as u16) {
                 let symbol2 = &self.symbols[code2 as usize];
                 // If either symbol is zero-length, or if merging would yield a symbol of
                 // length greater than 8, skip.
diff --git a/src/find_longest/naive.rs b/src/find_longest/naive.rs
index c75ecad..c9add2d 100644
--- a/src/find_longest/naive.rs
+++ b/src/find_longest/naive.rs
@@ -15,7 +15,7 @@ impl FindLongestSymbol for SymbolTable {
         // Start with the code corresponding to the escape of the first character in the text
         let mut best_code = text[0] as u16;
         let mut best_overlap = 1;
-        for code in 256..511 {
+        for code in 256..(256 + self.n_symbols as u16) {
             let symbol = &self.symbols[code as usize];
             if symbol.is_prefix(text) && symbol.len() > best_overlap {
                 best_code = code;