diff --git a/spec/runtime/helpers/spy_input.cc b/spec/runtime/helpers/spy_input.cc
index 8d7ebdaf..4e1020b6 100644
--- a/spec/runtime/helpers/spy_input.cc
+++ b/spec/runtime/helpers/spy_input.cc
@@ -8,7 +8,7 @@ using std::string;
 
 static const size_t UTF8_MAX_CHAR_SIZE = 4;
 
-static size_t string_char_count(const string &text) {
+size_t SpyInput::char_count(const string &text) {
   const char *bytes = text.data();
   size_t len = text.size();
   size_t character = 0, byte = 0;
@@ -102,7 +102,7 @@ TSInput SpyInput::input() {
 
 TSInputEdit SpyInput::replace(size_t start_char, size_t chars_removed, string text) {
   string text_removed = swap_substr(start_char, chars_removed, text);
-  size_t chars_inserted = string_char_count(text);
+  size_t chars_inserted = SpyInput::char_count(text);
   undo_stack.push_back(SpyInputEdit{start_char, chars_inserted, text_removed});
   return {start_char, chars_inserted, chars_removed};
 }
@@ -111,7 +111,7 @@ TSInputEdit SpyInput::undo() {
   SpyInputEdit entry = undo_stack.back();
   undo_stack.pop_back();
   swap_substr(entry.position, entry.chars_removed, entry.text_inserted);
-  size_t chars_inserted = string_char_count(entry.text_inserted);
+  size_t chars_inserted = SpyInput::char_count(entry.text_inserted);
   return TSInputEdit{entry.position, chars_inserted, entry.chars_removed};
 }
 
diff --git a/spec/runtime/helpers/spy_input.h b/spec/runtime/helpers/spy_input.h
index b2a0249c..a0b268b6 100644
--- a/spec/runtime/helpers/spy_input.h
+++ b/spec/runtime/helpers/spy_input.h
@@ -31,6 +31,8 @@ class SpyInput {
   TSInputEdit replace(size_t start_char, size_t chars_removed, std::string text);
   TSInputEdit undo();
 
+  static size_t char_count(const std::string &);
+
   std::string content;
   std::vector<std::string> strings_read;
 };
diff --git a/spec/runtime/language_specs.cc b/spec/runtime/language_specs.cc
index aa48b212..7967d5b7 100644
--- a/spec/runtime/language_specs.cc
+++ b/spec/runtime/language_specs.cc
@@ -145,8 +145,8 @@ describe("Languages", [&]() {
         std::set<std::pair<size_t, string>> insertions;
 
         for (size_t i = 0; i < 50; i++) {
-          size_t edit_position = random() % entry.input.size();
-          size_t deletion_size = random() % (entry.input.size() - edit_position);
+          size_t edit_position = random() % SpyInput::char_count(entry.input);
+          size_t deletion_size = random() % (SpyInput::char_count(entry.input) - edit_position);
           string inserted_text = random_words(random() % 4 + 1);
 
           if (insertions.insert({edit_position, inserted_text}).second) {