diff --git a/js/src/frontend/BinASTTokenReaderContext.cpp b/js/src/frontend/BinASTTokenReaderContext.cpp
index 8ab6a65b5c83..54e77daf7818 100644
--- a/js/src/frontend/BinASTTokenReaderContext.cpp
+++ b/js/src/frontend/BinASTTokenReaderContext.cpp
@@ -6,8 +6,9 @@
 
 #include "frontend/BinASTTokenReaderContext.h"
 
-#include "mozilla/Result.h"     // MOZ_TRY*
-#include "mozilla/ScopeExit.h"  // mozilla::MakeScopeExit
+#include "mozilla/IntegerTypeTraits.h"  // mozilla::MaxValue
+#include "mozilla/Result.h"             // MOZ_TRY*
+#include "mozilla/ScopeExit.h"          // mozilla::MakeScopeExit
 
 #include <string.h>  // memchr, memcmp, memmove
 
@@ -1785,8 +1786,15 @@ JS::Result<Ok> HuffmanTableImplementationGeneric<T>::init(
     JSContext* cx, size_t numberOfSymbols, uint8_t maxBitLength) {
   MOZ_ASSERT(this->implementation.template is<
              HuffmanTableUnreachable>());  // Make sure that we're initializing.
-  if (maxBitLength > MAX_BIT_LENGTH_IN_SATURATED_TABLE ||
-      numberOfSymbols > 256) {
+  if (
+      // If the bit length is too large, don't put it in a saturated table
+      // as this would need too much space.
+      maxBitLength > MAX_BIT_LENGTH_IN_SATURATED_TABLE ||
+      // If there are too many symbols, don't put it in a saturated table
+      // as indices  wouldn't fit into `InternalIndex` .
+      numberOfSymbols >
+          mozilla::MaxValue<typename HuffmanTableImplementationSaturated<
+              T>::InternalIndex>::value) {
     this->implementation = {
         mozilla::VariantType<HuffmanTableImplementationMap<T>>{}, cx};
     MOZ_TRY(this->implementation.template as<HuffmanTableImplementationMap<T>>()
diff --git a/js/src/frontend/BinASTTokenReaderContext.h b/js/src/frontend/BinASTTokenReaderContext.h
index af805da65db5..f9cb030e3c87 100644
--- a/js/src/frontend/BinASTTokenReaderContext.h
+++ b/js/src/frontend/BinASTTokenReaderContext.h
@@ -451,6 +451,12 @@ class HuffmanTableImplementationSaturated {
   Iterator begin() const { return Iterator(values.begin()); }
   Iterator end() const { return Iterator(values.end()); }
 
+ public:
+  // An index into table `values`.
+  // We use `uint8_t` instead of `size_t` to limit the space
+  // used by the table.
+  using InternalIndex = uint8_t;
+
  private:
   // The entries in this Huffman Table, sorted in the order of insertion.
   //
@@ -460,12 +466,11 @@ class HuffmanTableImplementationSaturated {
   Vector<HuffmanEntry<T>> values;
 
   // The entries in this Huffman table, prepared for lookup.
-  // The `size_t` argument is an index into `values`.
   //
   // Invariant (once `init*` has been called):
   // - Length is `1 << maxBitLength`.
   // - for all i, `saturated[i] < values.length()`
-  Vector<uint8_t> saturated;
+  Vector<InternalIndex> saturated;
 
   // The maximal bitlength of a value in this table.
   //