diff --git a/t/utf8len.lua b/t/utf8len.lua
new file mode 100644
index 00000000..cbc0063a
--- /dev/null
+++ b/t/utf8len.lua
@@ -0,0 +1,12 @@
+local text="あいうえおかきくけこさしすせそ"
+
+for i=1,string.len(text) do
+    for j=i,string.len(text) do
+        local len,err =utf8.len(text,i,j)
+        if len then
+            print(string.format("[%d:%d]=%d",i,j,len))
+        else
+            print(string.format("[%d:%d]=ERROR %s",i,j,err))
+        end
+    end
+end