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diff --git a/libmailutils/tests/fltcnt.c b/libmailutils/tests/fltcnt.c
new file mode 100644
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+++ b/libmailutils/tests/fltcnt.c
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+/*
+NAME
+  fltcnt - check how mu_filter_chain_create() changes the reference counter
+           of its input stream.
+
+DESCRIPTION
+  On success, mu_filter_chain_create shall increment the reference counter
+  if its "transport" argument by 1.  On error, the reference counter shall
+  remain unchanged.  Versions of mailutils prior to 2021-07-15 failed to
+  meet the latter requirement.
+  
+  The program checks how the input reference counter changes across two
+  calls to mu_filter_chain_create: one that succeeds and other that fails.
+  If the changes are as described above, it returns 0.  Otherwise it prints
+  a diagnostics message on standard error and returns 1.
+
+LICENSE
+  GNU Mailutils -- a suite of utilities for electronic mail
+  Copyright (C) 2021 Free Software Foundation, Inc.
+
+  GNU Mailutils is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 3, or (at your option)
+  any later version.
+
+  GNU Mailutils 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 General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with GNU Mailutils.  If not, see <http://www.gnu.org/licenses/>.
+*/  
+  
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+#include <stdlib.h>
+#include <mailutils/mailutils.h>
+#include <mailutils/sys/stream.h>
+
+int
+main (int argc, char **argv)
+{
+  mu_stream_t in, flt;
+  int rc;
+  char *fargv[] = { "7bit", "+", "7bit", NULL };
+  int init_ref_count;
+
+  /* Create input stream and increase its reference counter. */ 
+  MU_ASSERT (mu_stdio_stream_create (&in, MU_STDIN_FD, 0));
+  mu_stream_ref (in);
+  /* Save the initial reference counter. */
+  init_ref_count = in->ref_count;
+
+  /*
+   * First pass.
+   *
+   * Check if input reference counter increases by 1 after successfull
+   * call to mu_filter_chain_create.
+   */
+  
+  /* Create valid filter chain */
+  rc = mu_filter_chain_create (&flt, in,
+			       MU_FILTER_ENCODE,
+			       MU_STREAM_READ,
+			       MU_ARRAY_SIZE(fargv) - 1,
+			       (char**) fargv);
+  if (rc != 0)
+    {
+      mu_diag_funcall (MU_DIAG_ERROR, "first mu_filter_chain_create", NULL, rc);
+      return 1;
+    }
+
+  /* Check if ref_count value is as expected */
+  if (in->ref_count != init_ref_count + 1)
+    {
+      mu_error ("success filter: unexpected ref_count: %lu",
+		(unsigned long) in->ref_count);
+      return 1;
+    }
+
+  /* Destroy the filter and check if ref_count dropped to its initial value. */
+  mu_stream_destroy (&flt);
+      
+  if (in->ref_count != init_ref_count)
+    {
+      mu_error ("after destroying success filter: unexpected ref_count: %lu",
+		(unsigned long) in->ref_count);
+      return 1;
+    }
+
+  /*
+   * Second pass.
+   *
+   * Check if input reference counter remains unchanged after a failed
+   * call to mu_filter_chain_create.
+   */
+
+  /* Request unexisting filter. */
+  fargv[2] = "there_is_no_such_filter";
+  rc = mu_filter_chain_create (&flt, in,
+			       MU_FILTER_ENCODE,
+			       MU_STREAM_READ,
+			       MU_ARRAY_SIZE(fargv) - 1,
+			       (char**) fargv);
+  if (rc == 0)
+    {
+      mu_error ("second mu_filter_chain_create succeeded where it should not");
+      return 1;
+    }
+
+  if (in->ref_count != init_ref_count)
+    {
+      mu_error ("after failed filter attempt: unexpected ref_count: %lu",
+		(unsigned long) in->ref_count);
+      return 1;
+    }
+  
+  return 0;
+}
+
+