diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c
index 1df26c217f9a..a2b917dd60e5 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_selftests.c
@@ -1432,11 +1432,11 @@ static int __stmmac_test_l4filt(struct stmmac_priv *priv, u32 dst, u32 src,
 	struct {
 		struct flow_dissector_key_basic bkey;
 		struct flow_dissector_key_ports key;
-	} __aligned(BITS_PER_LONG / 8) keys;
+	} __aligned(BITS_PER_LONG / 8) keys = { };
 	struct {
 		struct flow_dissector_key_basic bmask;
 		struct flow_dissector_key_ports mask;
-	} __aligned(BITS_PER_LONG / 8) masks;
+	} __aligned(BITS_PER_LONG / 8) masks = { };
 	unsigned long dummy_cookie = 0xdeadbeef;
 	struct stmmac_packet_attrs attr = { };
 	struct flow_dissector *dissector;
@@ -1489,6 +1489,8 @@ static int __stmmac_test_l4filt(struct stmmac_priv *priv, u32 dst, u32 src,
 	keys.bkey.ip_proto = udp ? IPPROTO_UDP : IPPROTO_TCP;
 	keys.key.src = htons(src);
 	keys.key.dst = htons(dst);
+	/* Match the full IP proto field */
+	masks.bmask.ip_proto = 0xff;
 	masks.mask.src = src_mask;
 	masks.mask.dst = dst_mask;