diff --git a/project.gyp b/project.gyp
index 4e998048..f348a616 100644
--- a/project.gyp
+++ b/project.gyp
@@ -102,6 +102,7 @@
         'src/runtime/node.c',
         'src/runtime/parser.c',
         'src/runtime/stack.c',
+        'src/runtime/string_input.c',
         'src/runtime/tree.c',
       ],
       'cflags_c': [
diff --git a/src/runtime/document.c b/src/runtime/document.c
index a734998f..0f8a95af 100644
--- a/src/runtime/document.c
+++ b/src/runtime/document.c
@@ -3,7 +3,7 @@
 #include "runtime/tree.h"
 #include "runtime/node.h"
 #include "runtime/parser.h"
-#include <string.h>
+#include "runtime/string_input.h"
 
 struct TSDocument {
   TSParser parser;
@@ -59,41 +59,6 @@ const char *ts_document_symbol_name(const TSDocument *document,
   return document->parser.language->symbol_names[tree->symbol];
 }
 
-typedef struct {
-  const char *string;
-  size_t position;
-  size_t length;
-} TSStringInput;
-
-const char *ts_string_input_read(void *d, size_t *bytes_read) {
-  TSStringInput *data = (TSStringInput *)d;
-  if (data->position >= data->length) {
-    *bytes_read = 0;
-    return "";
-  }
-  size_t previous_position = data->position;
-  data->position = data->length;
-  *bytes_read = data->position - previous_position;
-  return data->string + previous_position;
-}
-
-int ts_string_input_seek(void *d, size_t position) {
-  TSStringInput *data = (TSStringInput *)d;
-  data->position = position;
-  return (position < data->length);
-}
-
-TSInput ts_string_input_make(const char *string) {
-  TSStringInput *data = malloc(sizeof(TSStringInput));
-  data->string = string;
-  data->position = 0;
-  data->length = strlen(string);
-  return (TSInput) { .data = (void *)data,
-                     .read_fn = ts_string_input_read,
-                     .seek_fn = ts_string_input_seek,
-                     .release_fn = free };
-}
-
 void ts_document_set_input_string(TSDocument *document, const char *text) {
   ts_document_set_input(document, ts_string_input_make(text));
 }
diff --git a/src/runtime/string_input.c b/src/runtime/string_input.c
new file mode 100644
index 00000000..f55ac36d
--- /dev/null
+++ b/src/runtime/string_input.c
@@ -0,0 +1,37 @@
+#include "runtime/string_input.h"
+#include <string.h>
+
+typedef struct {
+  const char *string;
+  size_t position;
+  size_t length;
+} TSStringInput;
+
+const char *ts_string_input_read(void *d, size_t *bytes_read) {
+  TSStringInput *data = (TSStringInput *)d;
+  if (data->position >= data->length) {
+    *bytes_read = 0;
+    return "";
+  }
+  size_t previous_position = data->position;
+  data->position = data->length;
+  *bytes_read = data->position - previous_position;
+  return data->string + previous_position;
+}
+
+int ts_string_input_seek(void *d, size_t position) {
+  TSStringInput *data = (TSStringInput *)d;
+  data->position = position;
+  return (position < data->length);
+}
+
+TSInput ts_string_input_make(const char *string) {
+  TSStringInput *data = malloc(sizeof(TSStringInput));
+  data->string = string;
+  data->position = 0;
+  data->length = strlen(string);
+  return (TSInput) { .data = (void *)data,
+                     .read_fn = ts_string_input_read,
+                     .seek_fn = ts_string_input_seek,
+                     .release_fn = free };
+}
diff --git a/src/runtime/string_input.h b/src/runtime/string_input.h
new file mode 100644
index 00000000..fe5e4b1f
--- /dev/null
+++ b/src/runtime/string_input.h
@@ -0,0 +1,16 @@
+#ifndef RUNTIME_STRING_INPUT_H_
+#define RUNTIME_STRING_INPUT_H_
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "tree_sitter/runtime.h"
+
+TSInput ts_string_input_make(const char *);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif  // RUNTIME_STRING_INPUT_H_