--- /dev/null
+/* Test flushing input file after ungetc (bug 5994).
+ 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-ungetc-fflush", &filename);
+ TEST_VERIFY_EXIT (fd != -1);
+ xclose (fd);
+
+ /* Test as in bug 5994. */
+ FILE *fp = xfopen (filename, "w");
+ TEST_VERIFY_EXIT (fputs ("#include", fp) >= 0);
+ xfclose (fp);
+ fp = xfopen (filename, "r");
+ TEST_COMPARE (fgetc (fp), '#');
+ TEST_COMPARE (fgetc (fp), 'i');
+ TEST_COMPARE (ungetc ('@', fp), '@');
+ TEST_COMPARE (fflush (fp), 0);
+ TEST_COMPARE (lseek (fileno (fp), 0, SEEK_CUR), 1);
+ TEST_COMPARE (fgetc (fp), 'i');
+ TEST_COMPARE (fgetc (fp), 'n');
+ xfclose (fp);
+
+ /* Test as in bug 12799 (duplicate of 5994). */
+ fp = xfopen (filename, "w+");
+ TEST_VERIFY_EXIT (fputs ("hello world", fp) >= 0);
+ rewind (fp);
+ TEST_VERIFY (fileno (fp) >= 0);
+ char buffer[10];
+ TEST_COMPARE (fread (buffer, 1, 5, fp), 5);
+ TEST_COMPARE (fgetc (fp), ' ');
+ TEST_COMPARE (ungetc ('@', fp), '@');
+ TEST_COMPARE (fflush (fp), 0);
+ TEST_COMPARE (fgetc (fp), ' ');
+ xfclose (fp);
+
+ return 0;
+}
+
+#include <support/test-driver.c>