diff --git a/setup.py b/setup.py
index d780b038a..453ea688f 100755
--- a/setup.py
+++ b/setup.py
@@ -473,17 +473,15 @@ class pil_build_ext(build_ext):
                 lib_root = include_root = root
 
             if lib_root is not None:
-                if isinstance(lib_root, str):
-                    _add_directory(library_dirs, lib_root)
-                else:
-                    for lib_dir in lib_root:
-                        _add_directory(library_dirs, lib_dir)
+                if not isinstance(lib_root, (tuple, list)):
+                    lib_root = (lib_root,)
+                for lib_dir in lib_root:
+                    _add_directory(library_dirs, lib_dir)
             if include_root is not None:
-                if isinstance(include_root, str):
-                    _add_directory(include_dirs, include_root)
-                else:
-                    for include_dir in include_root:
-                        _add_directory(include_dirs, include_dir)
+                if not isinstance(include_root, (tuple, list)):
+                    include_root = (include_root,)
+                for include_dir in include_root:
+                    _add_directory(include_dirs, include_dir)
 
         # respect CFLAGS/CPPFLAGS/LDFLAGS
         for k in ("CFLAGS", "CPPFLAGS", "LDFLAGS"):