diff --git a/sys/opencrypto/xform_chacha20_poly1305.c b/sys/opencrypto/xform_chacha20_poly1305.c
--- a/sys/opencrypto/xform_chacha20_poly1305.c
+++ b/sys/opencrypto/xform_chacha20_poly1305.c
@@ -55,7 +55,7 @@
 {
 	struct chacha20_poly1305_cipher_ctx *ctx = vctx;
 
-	KASSERT(ivlen == sizeof(ctx->nonce),
+	KASSERT(ivlen == 8 || ivlen == sizeof(ctx->nonce),
 	    ("%s: invalid nonce length", __func__));
 
 	/* Block 0 is used for the poly1305 key. */