diff --git a/spec/runtime/helpers/spy_reader.cc b/spec/runtime/helpers/spy_reader.cc
index 1aa34db0..d9b14fdf 100644
--- a/spec/runtime/helpers/spy_reader.cc
+++ b/spec/runtime/helpers/spy_reader.cc
@@ -26,18 +26,21 @@ SpyReader::SpyReader(string content, size_t chunk_size) :
     buffer(new char[chunk_size]),
     content(content),
     position(0),
-    chunk_size(chunk_size),
-    input({
-        this,
-        spy_read,
-        spy_seek,
-        nullptr,
-    }) {}
+    chunk_size(chunk_size) {}
 
 void SpyReader::clear() {
   strings_read.clear();
 }
 
+TSInput SpyReader::input() {
+  TSInput result;
+  result.data = this;
+  result.seek_fn = spy_seek;
+  result.read_fn = spy_read;
+  result.release_fn = nullptr;
+  return result;
+}
+
 SpyReader::~SpyReader() {
   delete buffer;
 }
diff --git a/spec/runtime/helpers/spy_reader.h b/spec/runtime/helpers/spy_reader.h
index c3578f3a..b583ab56 100644
--- a/spec/runtime/helpers/spy_reader.h
+++ b/spec/runtime/helpers/spy_reader.h
@@ -11,12 +11,12 @@ class SpyReader {
   ~SpyReader();
 
   void clear();
+  TSInput input();
 
   char *buffer;
   std::string content;
   size_t position;
   size_t chunk_size;
-  TSInput input;
   std::vector<std::string> strings_read;
 };
 
diff --git a/spec/runtime/parser_spec.cc b/spec/runtime/parser_spec.cc
index f499cc06..16a6425f 100644
--- a/spec/runtime/parser_spec.cc
+++ b/spec/runtime/parser_spec.cc
@@ -27,7 +27,7 @@ describe("Parser", [&]() {
 
   auto set_text = [&](const char *text) {
     reader = new SpyReader(text, chunk_size);
-    ts_document_set_input(doc, reader->input);
+    ts_document_set_input(doc, reader->input());
     root = ts_document_root_node(doc);
     reader->clear();
   };