diff --git a/libio/fileops.c b/libio/fileops.c
index 358378431f..97875d1eaf 100644
--- a/libio/fileops.c
+++ b/libio/fileops.c
@@ -1106,11 +1106,18 @@ _IO_file_seekoff_mmap (FILE *fp, off64_t offset, int dir, int mode)
   if (mode == 0)
     return fp->_offset - (fp->_IO_read_end - fp->_IO_read_ptr);
 
+  if (_IO_in_backup (fp))
+    {
+      if (dir == _IO_seek_cur)
+	offset += fp->_IO_read_ptr - fp->_IO_read_end;
+      _IO_switch_to_main_get_area (fp);
+    }
+
   switch (dir)
     {
     case _IO_seek_cur:
       /* Adjust for read-ahead (bytes is buffer). */
-      offset += fp->_IO_read_ptr - fp->_IO_read_base;
+      offset += fp->_offset - (fp->_IO_read_end - fp->_IO_read_ptr);
       break;
     case _IO_seek_set:
       break;
diff --git a/stdio-common/Makefile b/stdio-common/Makefile
index 48fbf05a85..06c9eaf426 100644
--- a/stdio-common/Makefile
+++ b/stdio-common/Makefile
@@ -261,6 +261,7 @@ tests := \
   tst-freopen64-7 \
   tst-freopen7 \
   tst-fseek \
+  tst-fseek-mmap \
   tst-fwrite \
   tst-fwrite-memstrm \
   tst-fwrite-overflow \
diff --git a/stdio-common/tst-fseek-mmap.c b/stdio-common/tst-fseek-mmap.c
new file mode 100644
index 0000000000..86fa99a1a2
--- /dev/null
+++ b/stdio-common/tst-fseek-mmap.c
@@ -0,0 +1,59 @@
+/* Test fseek on files using mmap (bug 32529).
+   Copyright (C) 2025 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+
+#include <support/check.h>
+#include <support/temp_file.h>
+#include <support/xstdio.h>
+#include <support/xunistd.h>
+
+int
+do_test (void)
+{
+  char *filename = NULL;
+  int fd = create_temp_file ("tst-fseek-mmap", &filename);
+  TEST_VERIFY_EXIT (fd != -1);
+  xclose (fd);
+
+  /* Test fseek after ungetc (bug 32529).  */
+  FILE *fp = xfopen (filename, "w");
+  TEST_VERIFY (0 <= fputs ("test", fp));
+  xfclose (fp);
+
+  fp = xfopen (filename, "rm");
+  TEST_COMPARE (fgetc (fp), 't');
+  TEST_COMPARE (ungetc ('u', fp), 'u');
+  TEST_COMPARE (fseek (fp, 0, SEEK_CUR), 0);
+  xfclose (fp);
+
+  /* Test fseek positioning after fflush (another issue covered by the
+     same fix).  */
+  fp = xfopen (filename, "rm");
+  TEST_COMPARE (fgetc (fp), 't');
+  TEST_COMPARE (fflush (fp), 0);
+  TEST_COMPARE (ftell (fp), 1);
+  TEST_COMPARE (fseek (fp, 0, SEEK_CUR), 0);
+  TEST_COMPARE (ftell (fp), 1);
+  TEST_COMPARE (fgetc (fp), 'e');
+  xfclose (fp);
+
+  return 0;
+}
+
+#include <support/test-driver.c>