diff --git a/src/ssl_crtlist.c b/src/ssl_crtlist.c
index 5296118..741e6ae 100644
--- a/src/ssl_crtlist.c
+++ b/src/ssl_crtlist.c
@@ -827,7 +827,10 @@
 		int comma = 0;
 
 		if (space) chunk_appendf(buf, " ");
-		chunk_appendf(buf, "alpn ");
+		if (len)
+			chunk_appendf(buf, "alpn ");
+		else
+			chunk_appendf(buf, "no-alpn");
 		while (len) {
 			unsigned short size;