diff --git a/ip/ipmaddr.c b/ip/ipmaddr.c
index 5683f6fa..46b86a3a 100644
--- a/ip/ipmaddr.c
+++ b/ip/ipmaddr.c
@@ -136,17 +136,18 @@ static void read_igmp(struct ma_info **result_p)
 
 	while (fgets(buf, sizeof(buf), fp)) {
 		struct ma_info *ma;
-		size_t len = 0;
 
 		if (buf[0] != '\t') {
+			size_t len;
+
 			sscanf(buf, "%d%s", &m.index, m.name);
 			len = strlen(m.name);
 			if (m.name[len - 1] == ':')
-				len--;
+				m.name[len - 1] = '\0';
 			continue;
 		}
 
-		if (filter.dev && strncmp(filter.dev, m.name, len))
+		if (filter.dev && strcmp(filter.dev, m.name))
 			continue;
 
 		sscanf(buf, "%08x%d", (__u32 *)&m.addr.data, &m.users);