diff --git a/libio/genops.c b/libio/genops.c
index 2197bfe7a1..e4378ca48f 100644
--- a/libio/genops.c
+++ b/libio/genops.c
@@ -730,6 +730,13 @@ _IO_flush_all (void)
 	   )
 	  && _IO_OVERFLOW (fp, EOF) == EOF)
 	result = EOF;
+      if (_IO_fileno (fp) >= 0
+	  && ((fp->_mode <= 0 && fp->_IO_read_ptr < fp->_IO_read_end)
+	      || (_IO_vtable_offset (fp) == 0
+		  && fp->_mode > 0 && (fp->_wide_data->_IO_read_ptr
+				       < fp->_wide_data->_IO_read_end)))
+	  && _IO_SYNC (fp) != 0)
+	result = EOF;
 
       _IO_funlockfile (fp);
       run_fp = NULL;
diff --git a/stdio-common/Makefile b/stdio-common/Makefile
index f6bdc32489..26c1b881cc 100644
--- a/stdio-common/Makefile
+++ b/stdio-common/Makefile
@@ -238,6 +238,7 @@ tests := \
   tst-fdopen \
   tst-fdopen2 \
   tst-ferror \
+  tst-fflush-all-input \
   tst-fgets \
   tst-fgets2 \
   tst-fileno \
diff --git a/stdio-common/tst-fflush-all-input.c b/stdio-common/tst-fflush-all-input.c
new file mode 100644
index 0000000000..8e3fca3a08
--- /dev/null
+++ b/stdio-common/tst-fflush-all-input.c
@@ -0,0 +1,94 @@
+/* Test fflush (NULL) flushes input files (bug 32369).
+   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 <stdlib.h>
+#include <unistd.h>
+#include <wchar.h>
+
+#include <support/check.h>
+#include <support/xstdio.h>
+#include <support/xunistd.h>
+
+int
+do_test (void)
+{
+  FILE *temp = tmpfile ();
+  TEST_VERIFY_EXIT (temp != NULL);
+  fprintf (temp, "abc");
+  TEST_COMPARE (fflush (temp), 0);
+  TEST_COMPARE (lseek (fileno (temp), 0, SEEK_SET), 0);
+  TEST_COMPARE (fgetc (temp), 'a');
+  TEST_COMPARE (fflush (NULL), 0);
+  TEST_COMPARE (lseek (fileno (temp), 0, SEEK_CUR), 1);
+  xfclose (temp);
+
+  /* Likewise, but in wide mode.  */
+  temp = tmpfile ();
+  TEST_VERIFY_EXIT (temp != NULL);
+  fwprintf (temp, L"abc");
+  TEST_COMPARE (fflush (temp), 0);
+  TEST_COMPARE (lseek (fileno (temp), 0, SEEK_SET), 0);
+  TEST_COMPARE (fgetwc (temp), L'a');
+  TEST_COMPARE (fflush (NULL), 0);
+  TEST_COMPARE (lseek (fileno (temp), 0, SEEK_CUR), 1);
+  xfclose (temp);
+
+  /* Similar tests, but with the flush implicitly occurring on exit
+     (in a forked subprocess).  */
+
+  temp = tmpfile ();
+  TEST_VERIFY_EXIT (temp != NULL);
+  pid_t pid = xfork ();
+  if (pid == 0)
+    {
+      fprintf (temp, "abc");
+      TEST_COMPARE (fflush (temp), 0);
+      TEST_COMPARE (lseek (fileno (temp), 0, SEEK_SET), 0);
+      TEST_COMPARE (fgetc (temp), 'a');
+      exit (EXIT_SUCCESS);
+    }
+  else
+    {
+      TEST_COMPARE (xwaitpid (pid, NULL, 0), pid);
+      TEST_COMPARE (lseek (fileno (temp), 0, SEEK_CUR), 1);
+      xfclose (temp);
+    }
+
+  temp = tmpfile ();
+  TEST_VERIFY_EXIT (temp != NULL);
+  pid = xfork ();
+  if (pid == 0)
+    {
+      fwprintf (temp, L"abc");
+      TEST_COMPARE (fflush (temp), 0);
+      TEST_COMPARE (lseek (fileno (temp), 0, SEEK_SET), 0);
+      TEST_COMPARE (fgetwc (temp), L'a');
+      exit (EXIT_SUCCESS);
+    }
+  else
+    {
+      TEST_COMPARE (xwaitpid (pid, NULL, 0), pid);
+      TEST_COMPARE (lseek (fileno (temp), 0, SEEK_CUR), 1);
+      xfclose (temp);
+    }
+
+  return 0;
+}
+
+#include <support/test-driver.c>