--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -2468,6 +2468,8 @@ class MiscIOTest(unittest.TestCase):
             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)

--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -83,6 +83,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #12175: FileIO.readall() now raises a ValueError instead of an IOError
+  if the file is closed.
+
 - Issue #1441530: In imaplib, use makefile() to wrap the SSL socket to avoid
   heap fragmentation and MemoryError with some malloc implementations.
 

--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -539,6 +539,8 @@ fileio_readall(fileio *self)
     Py_ssize_t total = 0;
     int n;
 
+    if (self->fd < 0)
+        return err_closed();
     if (!_PyVerify_fd(self->fd))
         return PyErr_SetFromErrno(PyExc_IOError);