diff --git a/ChangeLog b/ChangeLog
index 6151e4fd..34231bcc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2008-08-26  Nicolas François  <nicolas.francois@centraliens.net>
+
+	* src/groupmems.c: When removing an user, check if deluser is on
+	the list, not adduser. This fixes a segmentation fault for every
+	call of groupmems -d.
+	* libmisc/list.c: Add assertions to help identifying these issues.
+	* libmisc/list.c: Avoid implicit conversion of pointers to
+	booleans.
+
 2008-08-26  Nicolas François  <nicolas.francois@centraliens.net>
 
 	* NEWS, src/groupmems.c: Use the "groupmems" PAM service name
diff --git a/NEWS b/NEWS
index c60f0d25..19500726 100644
--- a/NEWS
+++ b/NEWS
@@ -18,6 +18,7 @@ shadow-4.1.2.1 -> shadow-4.1.3						UNRELEASED
     group.
   * Added syslog support.
   * Use the groupmems PAM service name instead of groupmod.
+  * Fix segmentation faults when adding or removing users from a group.
 - newusers
   * Implement the -r, --system option.
 - passwd
diff --git a/libmisc/list.c b/libmisc/list.c
index 36b3caf2..1d0525da 100644
--- a/libmisc/list.c
+++ b/libmisc/list.c
@@ -50,6 +50,8 @@ char **add_list (char **list, const char *member)
 	int i;
 	char **tmp;
 
+	assert (NULL != member);
+
 	/*
 	 * Scan the list for the new name.  Return the original list
 	 * pointer if it is present.
@@ -97,6 +99,8 @@ char **del_list (char **list, const char *member)
 	int i, j;
 	char **tmp;
 
+	assert (NULL != member);
+
 	/*
 	 * Scan the list for the old name.  Return the original list
 	 * pointer if it is not present.
@@ -142,12 +146,12 @@ char **dup_list (char *const *list)
 	int i;
 	char **tmp;
 
-	for (i = 0; list[i]; i++);
+	for (i = 0; NULL != list[i]; i++);
 
 	tmp = (char **) xmalloc ((i + 1) * sizeof (char *));
 
 	i = 0;
-	while (*list) {
+	while (NULL != *list) {
 		tmp[i] = xstrdup (*list);
 		i++;
 		list++;
@@ -159,12 +163,15 @@ char **dup_list (char *const *list)
 
 bool is_on_list (char *const *list, const char *member)
 {
-	while (*list) {
+	assert (NULL != member);
+
+	while (NULL != *list) {
 		if (strcmp (*list, member) == 0) {
 			return true;
 		}
 		list++;
 	}
+
 	return false;
 }
 
@@ -179,6 +186,8 @@ char **comma_to_list (const char *comma)
 	int i;
 	char *cp, *cp2;
 
+	assert (NULL != comma);
+
 	/*
 	 * Make a copy since we are going to be modifying the list
 	 */
diff --git a/src/groupmems.c b/src/groupmems.c
index c1f083de..b659fe19 100644
--- a/src/groupmems.c
+++ b/src/groupmems.c
@@ -291,7 +291,7 @@ int main (int argc, char **argv)
 			fail_exit (13);
 		}
 	} else if (NULL != deluser) {
-		if (!is_on_list (grp->gr_mem, adduser)) {
+		if (!is_on_list (grp->gr_mem, deluser)) {
 			fprintf (stderr,
 			         _("%s: user '%s' is not a member of '%s'\n"),
 			         Prog, deluser, grp->gr_name);