diff --git a/Doc/library/io.rst b/Doc/library/io.rst
index 748c49968f505c1..b0585c35705530b 100644
--- a/Doc/library/io.rst
+++ b/Doc/library/io.rst
@@ -405,7 +405,9 @@ I/O Base Classes
 
    .. method:: seek(offset, whence=os.SEEK_SET, /)
 
-      Change the stream position to the given byte *offset*,
+      Change the stream position to the given *offset*,
+      treated as a byte offset for binary streams
+      and a character offset for text streams,
       interpreted relative to the position indicated by *whence*,
       and return the new absolute position.
       Values for *whence* are:
diff --git a/Modules/_io/clinic/iobase.c.h b/Modules/_io/clinic/iobase.c.h
index a35cac7dc0b8d7e..9f6ca457e581253 100644
--- a/Modules/_io/clinic/iobase.c.h
+++ b/Modules/_io/clinic/iobase.c.h
@@ -12,13 +12,16 @@ PyDoc_STRVAR(_io__IOBase_seek__doc__,
 "seek($self, offset, whence=os.SEEK_SET, /)\n"
 "--\n"
 "\n"
-"Change the stream position to the given byte offset.\n"
+"Change the stream position to the given offset.\n"
 "\n"
 "  offset\n"
 "    The stream position, relative to \'whence\'.\n"
 "  whence\n"
 "    The relative position to seek from.\n"
 "\n"
+"The offset is treated as a byte offset for binary streams, and as a\n"
+"character offset for text streams.\n"
+"\n"
 "The offset is interpreted relative to the position indicated by whence.\n"
 "Values for whence are:\n"
 "\n"
@@ -441,4 +444,4 @@ _io__RawIOBase_readall(PyObject *self, PyObject *Py_UNUSED(ignored))
 {
     return _io__RawIOBase_readall_impl(self);
 }
-/*[clinic end generated code: output=dab5e9323d191e32 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=08641f02df89a459 input=a9049054013a1b77]*/
diff --git a/Modules/_io/iobase.c b/Modules/_io/iobase.c
index 184e0b7d1aa7f1a..3031817a8dc396e 100644
--- a/Modules/_io/iobase.c
+++ b/Modules/_io/iobase.c
@@ -97,7 +97,10 @@ _io._IOBase.seek
       The relative position to seek from.
     /
 
-Change the stream position to the given byte offset.
+Change the stream position to the given offset.
+
+The offset is treated as a byte offset for binary streams, and as a
+character offset for text streams.
 
 The offset is interpreted relative to the position indicated by whence.
 Values for whence are:
@@ -112,7 +115,7 @@ Return the new absolute position.
 static PyObject *
 _io__IOBase_seek_impl(PyObject *self, PyTypeObject *cls,
                       int Py_UNUSED(offset), int Py_UNUSED(whence))
-/*[clinic end generated code: output=8bd74ea6538ded53 input=74211232b363363e]*/
+/*[clinic end generated code: output=8bd74ea6538ded53 input=2e7053a15733b5d6]*/
 {
     _PyIO_State *state = get_io_state_by_cls(cls);
     return iobase_unsupported(state, "seek");