diff --git a/src/json_store/__init__.py b/src/json_store/__init__.py
index bc9bef4..82e2e1b 100644
--- a/src/json_store/__init__.py
+++ b/src/json_store/__init__.py
@@ -1,5 +1,5 @@
 from .json_store import JSONStore
 
-__version__ = "4.0"
+__version__ = "4.1"
 
 open = JSONStore
diff --git a/src/json_store/shelve2json.py b/src/json_store/shelve2json.py
index 99b9796..797d237 100644
--- a/src/json_store/shelve2json.py
+++ b/src/json_store/shelve2json.py
@@ -9,13 +9,17 @@
 import json_store
 
 
-def convert(oldfile):
+def convert(oldfile: str):
     if not os.path.isfile(oldfile):
         raise ValueError("No such file: {}".format(oldfile))
 
-    data = shelve.open(oldfile)
+    name = oldfile
+    # remove extensions that are implicitly added by the underlying DBM module
+    name = name.rsplit(".dat")[0]  # Windows
+    name = name.rsplit(".db")[0]  # macOS
 
-    newfile = oldfile.rsplit(".db")[0] + ".json"
+    data = shelve.open(name)
+    newfile = name + ".json"
     store = json_store.open(newfile)
     store.update(data)
     store.sync()
diff --git a/tests/test_shelve2json.sh b/tests/test_shelve2json.sh
index 36abfae..44e20d8 100644
--- a/tests/test_shelve2json.sh
+++ b/tests/test_shelve2json.sh
@@ -1,8 +1,20 @@
-#!/bin/sh
+#!/usr/bin/env bash
 set -e -x
 
-tmp=$(mktemp)
+tmp=$(mktemp tmpXXXXX)
+uname -s
 rm -f "$tmp"
-python -c 'import shelve; db=shelve.open("'"$tmp"'", flag="n"); db["eggs"] = "eggs"; db.close()'
-shelve2json "$tmp"
-rm -f "$tmp" "$tmp.json"
+python3 -c 'import shelve; db=shelve.open("'"$tmp"'", flag="n"); db["eggs"] = "eggs"; db.sync(); db.close()'
+
+if [[ -s "$tmp".dat ]]; then
+	# Windows
+	shelve2json "$tmp".dat
+elif [[ -s "$tmp".db ]]; then
+	# macOS
+	shelve2json "$tmp".db
+else
+	# Linux
+	shelve2json "$tmp"
+fi
+
+rm -f "$tmp" "$tmp".{dat,db,json}