diff --git a/importlib_resources/__init__.py b/importlib_resources/__init__.py
index b8d609f..fcb31b3 100644
--- a/importlib_resources/__init__.py
+++ b/importlib_resources/__init__.py
@@ -8,12 +8,12 @@
     read_binary,
     open_text,
     read_text,
+    is_resource,
 )
 
 from importlib_resources._py3 import (
     Package,
     Resource,
-    is_resource,
     path,
 )
 from importlib_resources.abc import ResourceReader
diff --git a/importlib_resources/_common.py b/importlib_resources/_common.py
index 838a993..5e7da81 100644
--- a/importlib_resources/_common.py
+++ b/importlib_resources/_common.py
@@ -165,3 +165,15 @@ def contents(package: Package) -> Iterable[str]:
     to check if it is a resource or not.
     """
     return [path.name for path in files(package).iterdir()]
+
+
+def is_resource(package: Package, name: str) -> bool:
+    """True if `name` is a resource inside `package`.
+
+    Directories are *not* resources.
+    """
+    resource = normalize_path(name)
+    for traversable in files(package).iterdir():
+        if traversable.name == resource:
+            return traversable.is_file()
+    return False
diff --git a/importlib_resources/_py3.py b/importlib_resources/_py3.py
index 43dce10..3a791fc 100644
--- a/importlib_resources/_py3.py
+++ b/importlib_resources/_py3.py
@@ -51,22 +51,6 @@ def _path_from_open_resource(reader, resource):
     return _common._tempfile(saved.read, suffix=resource)
 
 
-def is_resource(package: Package, name: str) -> bool:
-    """True if `name` is a resource inside `package`.
-
-    Directories are *not* resources.
-    """
-    package = _common.get_package(package)
-    _common.normalize_path(name)
-    reader = _common.get_resource_reader(package)
-    if reader is not None:
-        return reader.is_resource(name)
-    package_contents = set(_common.contents(package))
-    if name not in package_contents:
-        return False
-    return (_common.from_package(package) / name).is_file()
-
-
 @singledispatch
 def _ensure_sequence(iterable):
     return list(iterable)