diff --git a/tools/ebpf/mark_packet_id.c b/tools/ebpf/mark_packet_id.c
index aadfe7b..57b7747 100644
--- a/tools/ebpf/mark_packet_id.c
+++ b/tools/ebpf/mark_packet_id.c
@@ -5,21 +5,29 @@
 #define PACKET_ID_MASK 0x0FFFFFFF
 #define VERDICT_MASK 0xF0000000
 
+struct counter_state {
+  struct bpf_spin_lock lock;
+  __u32 value;
+};
+
 struct {
   __uint(type, BPF_MAP_TYPE_ARRAY);
   __uint(max_entries, 1);
   __type(key, __u32);
-  __type(value, __u32);
+  __type(value, struct counter_state);
 } packet_counter SEC(".maps");
 
 SEC("classifier")
 int classifier(struct __sk_buff *skb) {
   __u32 key = 0;
-  __u32 *counter = bpf_map_lookup_elem(&packet_counter, &key);
+  struct counter_state *state = bpf_map_lookup_elem(&packet_counter, &key);
   __u32 next = 1;
 
-  if (counter) {
-    next = __sync_add_and_fetch(counter, 1);
+  if (state) {
+    bpf_spin_lock(&state->lock);
+    state->value += 1;
+    next = state->value;
+    bpf_spin_unlock(&state->lock);
   }
 
   skb->mark = (skb->mark & VERDICT_MASK) | (next & PACKET_ID_MASK);