diff --git a/lib/mu-flags.c b/lib/mu-flags.c
index 4c66002c..bd9ee667 100644
--- a/lib/mu-flags.c
+++ b/lib/mu-flags.c
@@ -1,5 +1,5 @@
 /*
-** Copyright (C) 2011  <djcb@djcbsoftware.nl>
+** Copyright (C) 2011-2012  <djcb@djcbsoftware.nl>
 **
 ** This program is free software; you can redistribute it and/or modify it
 ** under the terms of the GNU General Public License as published by the
@@ -16,6 +16,8 @@
 ** Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 **
 */
+
+#include <string.h>
 #include "mu-flags.h"
 
 struct _FlagInfo {
@@ -191,6 +193,36 @@ mu_flags_from_str (const char *str, MuFlagType types,
 
 
 
+char*
+mu_flags_custom_from_str (const char *str)
+{
+	char *custom;
+	const char* cur;
+	unsigned u;
+
+	g_return_val_if_fail (str, NULL);
+
+	for (cur = str, u = 0, custom = NULL; *cur; ++cur) {
+
+		MuFlags flag;
+		flag = mu_flag_from_char (*cur);
+
+		/* if it's a valid file flag, ignore it */
+		if (flag != MU_FLAG_INVALID &&
+		    mu_flag_type (flag) == MU_FLAG_TYPE_MAILFILE)
+			continue;
+
+		/* otherwise, add it to our custom string */
+		if (!custom)
+			custom = g_new0 (char, strlen(str) + 1);
+		custom[u++] = *cur;
+	}
+
+	return custom;
+}
+
+
+
 void
 mu_flags_foreach (MuFlagsForeachFunc func, gpointer user_data)
 {
diff --git a/lib/mu-flags.h b/lib/mu-flags.h
index 62020d98..3bc0205b 100644
--- a/lib/mu-flags.h
+++ b/lib/mu-flags.h
@@ -114,7 +114,7 @@ const char* mu_flags_to_str_s (MuFlags flags, MuFlagType types);
 /**
  * Get the (OR'ed) flags corresponding to a string representation
  *
- * @param str the string representation
+ * @param str the file info string
  * @param types the flag types to accept (other will be ignored)
  * @param ignore invalid if TRUE, ignore invalid flags, otherwise return
  * MU_FLAG_INVALID if an invalid flag is encountered
@@ -124,6 +124,19 @@ const char* mu_flags_to_str_s (MuFlags flags, MuFlagType types);
 MuFlags mu_flags_from_str (const char *str, MuFlagType types,
 			   gboolean ignore_invalid);
 
+
+/**
+ * return the concatenation of all non-standard file flags in str
+ * (ie., characters other than DFPRST) as a newly allocated string.
+ *
+ * @param str the file info string
+ *
+ * @return concatenation of all non-standard flags, as a string; free
+ * with g_free when done. If there are no such flags, return NULL.
+ */
+char*  mu_flags_custom_from_str (const char *str) G_GNUC_WARN_UNUSED_RESULT;
+
+
 /**
  * Update #oldflags with the flags in #str, where #str consists of the
  * the normal flag characters, but prefixed with either '+' or '-',
@@ -141,8 +154,6 @@ MuFlags mu_flags_from_str_delta (const char *str, MuFlags oldflags,
 				 MuFlagType types);
 
 
-
-
 typedef void (*MuFlagsForeachFunc) (MuFlags flag, gpointer user_data);
 
 /**
diff --git a/lib/tests/test-mu-flags.c b/lib/tests/test-mu-flags.c
index 464f959e..6296b6f8 100644
--- a/lib/tests/test-mu-flags.c
+++ b/lib/tests/test-mu-flags.c
@@ -137,11 +137,33 @@ test_mu_flags_from_str_delta (void)
 						   MU_FLAG_SIGNED | MU_FLAG_DRAFT,
 						   MU_FLAG_TYPE_ANY),==,
 			  MU_FLAG_PASSED | MU_FLAG_SEEN | MU_FLAG_SIGNED);
+}
 
-	/* g_assert_cmpuint (mu_flags_from_str_delta ("foobar", */
-	/* 					   MU_FLAG_INVALID, */
-	/* 					   MU_FLAG_TYPE_ANY),==, */
-	/* 		  MU_FLAG_INVALID); */
+
+static void
+test_mu_flags_custom_from_str (void)
+{
+	unsigned u;
+
+	struct {
+		const char *str;
+		const char *expected;
+	} cases[] = {
+		{ "ABC", "ABC" },
+		{ "PAF", "A" },
+		{ "ShelloPwoFrDldR123", "helloworld123" },
+		{ "SPD", NULL }
+	};
+
+	for (u = 0; u != G_N_ELEMENTS(cases); ++u) {
+		char *cust;
+		cust = mu_flags_custom_from_str (cases[u].str);
+		if (g_test_verbose())
+			g_print ("%s: str:%s; got:%s; expected:%s\n",
+				 __FUNCTION__, cases[u].str, cust, cases[u].expected);
+		g_assert_cmpstr (cust, ==, cases[u].expected);
+		g_free (cust);
+	}
 }
 
 
@@ -158,6 +180,8 @@ main (int argc, char *argv[])
 	g_test_add_func ("/mu-flags/test-mu-flags-to-str-s",test_mu_flags_to_str_s);
 	g_test_add_func ("/mu-flags/test-mu-flags-from-str",test_mu_flags_from_str);
 	g_test_add_func ("/mu-flags/test-mu-flags-from-str-delta",test_mu_flags_from_str_delta );
+	g_test_add_func ("/mu-flags/test-mu-flags-custom-from-str",
+			 test_mu_flags_custom_from_str);
 
 	g_log_set_handler (NULL,
 			   G_LOG_LEVEL_MASK | G_LOG_FLAG_FATAL| G_LOG_FLAG_RECURSION,