diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index 513354e928cb..d73cd247f8cd 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -1237,7 +1237,13 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr,
 		memset(__skb_push(skb, hh_len), 0, hh_len);
 	}
 
-	if (kattr->test.flags & BPF_F_TEST_SKB_CHECKSUM_COMPLETE) {
+	/*
+	 * A helper such as bpf_skb_change_tail() may have downgraded the skb
+	 * from CHECKSUM_COMPLETE. skb->csum is then unused by the stack and
+	 * there is nothing to validate.
+	 */
+	if ((kattr->test.flags & BPF_F_TEST_SKB_CHECKSUM_COMPLETE) &&
+	    skb->ip_summed == CHECKSUM_COMPLETE) {
 		const int off = skb_network_offset(skb);
 		int len = skb->len - off;
 		__wsum csum;