diff --git a/spec/runtime/languages/arithmetic/main.txt b/spec/runtime/languages/arithmetic/main.txt
index 4a5a9726..f6c75dd1 100644
--- a/spec/runtime/languages/arithmetic/main.txt
+++ b/spec/runtime/languages/arithmetic/main.txt
@@ -12,6 +12,13 @@ x
 ---
 (variable)
 
+====================================
+parses variables with greek letters
+====================================
+φ1
+---
+(variable)
+
 ===================
 parses products
 ===================
diff --git a/spec/runtime/parser_spec.cc b/spec/runtime/parser_spec.cc
index fc53bb2b..4bb0195c 100644
--- a/spec/runtime/parser_spec.cc
+++ b/spec/runtime/parser_spec.cc
@@ -33,13 +33,13 @@ describe("Parser", [&]() {
   };
 
   auto insert_text = [&](size_t position, string text) {
-    reader->content.insert(position, text);
+    AssertThat(reader->insert(position, text), IsTrue());
     ts_document_edit(doc, { position, 0, text.length() });
     root = ts_document_root_node(doc);
   };
 
   auto delete_text = [&](size_t position, size_t length) {
-    reader->content.erase(position, length);
+    AssertThat(reader->erase(position, length), IsTrue());
     ts_document_edit(doc, { position, length, 0 });
     root = ts_document_root_node(doc);
   };
@@ -284,6 +284,26 @@ describe("Parser", [&]() {
           ts_node_release(node);
         });
       });
+
+      describe("with non-ascii characters", [&]() {
+        before_each([&]() {
+          chunk_size = 50;
+
+          // αβδ + 1
+          set_text("\u03b1\u03b2\u03b4 + 1");
+
+          AssertThat(ts_node_string(root), Equals(
+              "(DOCUMENT (sum (variable) (number)))"));
+
+          // αβδ + ψ1
+          insert_text(strlen("abd + "), "\u03c8");
+        });
+
+        it("inserts the text according to the UTF8 character index", [&]() {
+          AssertThat(ts_node_string(root), Equals(
+              "(DOCUMENT (sum (variable) (variable)))"));
+        });
+      });
     });
 
     describe("deleting text", [&]() {