diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 8af8a64..9b18b70 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -2468,6 +2468,8 @@
             self.assertRaises(ValueError, f.read)
             if hasattr(f, "read1"):
                 self.assertRaises(ValueError, f.read1, 1024)
+            if hasattr(f, "readall"):
+                self.assertRaises(ValueError, f.readall)
             if hasattr(f, "readinto"):
                 self.assertRaises(ValueError, f.readinto, bytearray(1024))
             self.assertRaises(ValueError, f.readline)