diff --git a/alias.c b/alias.c
index 57495fb95..0e12a0f92 100644
--- a/alias.c
+++ b/alias.c
@@ -52,6 +52,7 @@ __unused static const char rcsid[] = "$Sudo$";
  * Globals
  */
 struct rbtree *aliases;
+unsigned int alias_seqno;
 
 /*
  * Local protoypes
@@ -91,11 +92,22 @@ find_alias(name, type)
 {
     struct alias key;
     struct rbnode *node;
+    struct alias *a = NULL;
 
     key.name = name;
     key.type = type;
-    node = rbfind(aliases, &key);
-    return(node ? node->data : NULL);
+    if ((node = rbfind(aliases, &key)) != NULL) {
+	    /*
+	     * Compare the global sequence number with the one stored
+	     * in the alias.  If they match then we've seen this alias
+	     * before and found a loop.
+	     */
+	    a = node->data;
+	    if (a->seqno == alias_seqno)
+		return(NULL);
+	    a->seqno = alias_seqno;
+    }
+    return(a);
 }
 
 /*
@@ -114,6 +126,7 @@ alias_add(name, type, members)
     a = emalloc(sizeof(*a));
     a->name = name;
     a->type = type;
+    a->seqno = 0;
     list2tq(&a->members, members);
     if (rbinsert(aliases, a)) {
 	efree(a);
diff --git a/match.c b/match.c
index fc9fd5127..5a31e0038 100644
--- a/match.c
+++ b/match.c
@@ -102,8 +102,8 @@ __unused static const char rcsid[] = "$Sudo$";
  * Check for user described by pw in a list of members.
  * Returns ALLOW, DENY or UNSPEC.
  */
-int
-userlist_matches(pw, list)
+static int
+_userlist_matches(pw, list)
     struct passwd *pw;
     struct member_list *list;
 {
@@ -126,7 +126,7 @@ userlist_matches(pw, list)
 		break;
 	    case ALIAS:
 		if ((a = find_alias(m->name, USERALIAS)) != NULL) {
-		    rval = userlist_matches(pw, &a->members);
+		    rval = _userlist_matches(pw, &a->members);
 		    if (rval != UNSPEC)
 			matched = m->negated ? !rval : rval;
 		    break;
@@ -143,13 +143,22 @@ userlist_matches(pw, list)
     return(matched);
 }
 
+int
+userlist_matches(pw, list)
+    struct passwd *pw;
+    struct member_list *list;
+{
+    alias_seqno++;
+    return(_userlist_matches(pw, list));
+}
+
 /*
  * Check for user described by pw in a list of members.
  * If list is NULL compare against def_runas_default.
  * Returns ALLOW, DENY or UNSPEC.
  */
-int
-runaslist_matches(list)
+static int
+_runaslist_matches(list)
     struct member_list *list;
 {
     struct member *m;
@@ -174,7 +183,7 @@ runaslist_matches(list)
 		break;
 	    case ALIAS:
 		if ((a = find_alias(m->name, RUNASALIAS)) != NULL) {
-		    rval = runaslist_matches(&a->members);
+		    rval = _runaslist_matches(&a->members);
 		    if (rval != UNSPEC)
 			matched = m->negated ? !rval : rval;
 		    break;
@@ -191,12 +200,20 @@ runaslist_matches(list)
     return(matched);
 }
 
+int
+runaslist_matches(list)
+    struct member_list *list;
+{
+    alias_seqno++;
+    return(_runaslist_matches(list));
+}
+
 /*
  * Check for host and shost in a list of members.
  * Returns ALLOW, DENY or UNSPEC.
  */
-int
-hostlist_matches(list)
+static int
+_hostlist_matches(list)
     struct member_list *list;
 {
     struct member *m;
@@ -218,7 +235,7 @@ hostlist_matches(list)
 		break;
 	    case ALIAS:
 		if ((a = find_alias(m->name, HOSTALIAS)) != NULL) {
-		    rval = hostlist_matches(&a->members);
+		    rval = _hostlist_matches(&a->members);
 		    if (rval != UNSPEC)
 			matched = m->negated ? !rval : rval;
 		    break;
@@ -235,6 +252,43 @@ hostlist_matches(list)
     return(matched);
 }
 
+int
+hostlist_matches(list)
+    struct member_list *list;
+{
+    alias_seqno++;
+    return(_hostlist_matches(list));
+}
+
+/*
+ * Check for cmnd and args in a list of members.
+ * Returns ALLOW, DENY or UNSPEC.
+ */
+static int
+_cmndlist_matches(list)
+    struct member_list *list;
+{
+    struct member *m;
+    int rval, matched = UNSPEC;
+
+    tq_foreach_rev(list, m) {
+	rval = cmnd_matches(m);
+	if (rval != UNSPEC) {
+	    matched = m->negated ? !rval : rval;
+	    break;
+	}
+    }
+    return(matched);
+}
+
+int
+cmndlist_matches(list)
+    struct member_list *list;
+{
+    alias_seqno++;
+    return(_cmndlist_matches(list));
+}
+
 /*
  * Check cmnd and args.
  * Returns ALLOW, DENY or UNSPEC.
@@ -252,8 +306,9 @@ cmnd_matches(m)
 	    matched = !m->negated;
 	    break;
 	case ALIAS:
+	    alias_seqno++;
 	    if ((a = find_alias(m->name, CMNDALIAS)) != NULL) {
-		rval = cmndlist_matches(&a->members);
+		rval = _cmndlist_matches(&a->members);
 		if (rval != UNSPEC)
 		    matched = m->negated ? !rval : rval;
 	    }
@@ -267,27 +322,6 @@ cmnd_matches(m)
     return(matched);
 }
 
-/*
- * Check for cmnd and args in a list of members.
- * Returns ALLOW, DENY or UNSPEC.
- */
-int
-cmndlist_matches(list)
-    struct member_list *list;
-{
-    struct member *m;
-    int rval, matched = UNSPEC;
-
-    tq_foreach_rev(list, m) {
-	rval = cmnd_matches(m);
-	if (rval != UNSPEC) {
-	    matched = m->negated ? !rval : rval;
-	    break;
-	}
-    }
-    return(matched);
-}
-
 /*
  * If path doesn't end in /, return TRUE iff cmnd & path name the same inode;
  * otherwise, return TRUE if user_cmnd names one of the inodes in path.
diff --git a/parse.c b/parse.c
index ffe7c910a..9a3af430b 100644
--- a/parse.c
+++ b/parse.c
@@ -464,7 +464,7 @@ display_cmnd(v, pw)
  * Print the contents of a struct member to stdout
  */
 static void
-print_member(lbuf, name, type, negated, alias_type)
+_print_member(lbuf, name, type, negated, alias_type)
     struct lbuf *lbuf;
     char *name;
     int type, negated, alias_type;
@@ -492,7 +492,7 @@ print_member(lbuf, name, type, negated, alias_type)
 		tq_foreach_fwd(&a->members, m) {
 		    if (m != tq_first(&a->members))
 			lbuf_append(lbuf, ", ", NULL);
-		    print_member(lbuf, m->name, m->type,
+		    _print_member(lbuf, m->name, m->type,
 			negated ? !m->negated : m->negated, alias_type);
 		}
 		break;
@@ -503,3 +503,13 @@ print_member(lbuf, name, type, negated, alias_type)
 	    break;
     }
 }
+
+static void
+print_member(lbuf, name, type, negated, alias_type)
+    struct lbuf *lbuf;
+    char *name;
+    int type, negated, alias_type;
+{
+    alias_seqno++;
+    _print_member(lbuf, name, type, negated, alias_type);
+}
diff --git a/parse.h b/parse.h
index ebc6b12a0..2ae610ef9 100644
--- a/parse.h
+++ b/parse.h
@@ -119,6 +119,7 @@ struct member {
 struct alias {
     char *name;				/* alias name */
     int type; 				/* {USER,HOST,RUNAS,CMND}ALIAS */
+    unsigned int seqno;			/* sequence number */
     struct member_list members;		/* list of alias members */
 };
 
@@ -140,6 +141,11 @@ struct defaults {
 extern struct userspec_list userspecs;
 extern struct defaults_list defaults;
 
+/*
+ * Alias sequence number to avoid loops.
+ */
+extern unsigned int alias_seqno;
+
 /*
  * Prototypes
  */