diff --git a/lib/http_negotiate.c b/lib/http_negotiate.c
index 6e882a337eae85525195a0f11192c0d5ea645134..6a4b8660f7ec20d9b2c24e9798c28a2f1d18483e 100644
--- a/lib/http_negotiate.c
+++ b/lib/http_negotiate.c
@@ -101,8 +101,11 @@ CURLcode Curl_input_negotiate(struct connectdata *conn, bool proxy,
     if(result)
       return result;
 
-    if(!rawlen)
+    if(!rawlen) {
+      infof(data, "Negotiate handshake failure (empty challenge message)\n");
+
       return CURLE_BAD_CONTENT_ENCODING;
+    }
 
     input_token.length = rawlen;
 
diff --git a/lib/http_negotiate_sspi.c b/lib/http_negotiate_sspi.c
index 7afd609579fe7a62bbbc753f1f3e75476dab3fd5..e6ab0b78da494467520466566428a6ba1564eaac 100644
--- a/lib/http_negotiate_sspi.c
+++ b/lib/http_negotiate_sspi.c
@@ -168,8 +168,12 @@ CURLcode Curl_input_negotiate(struct connectdata *conn, bool proxy,
     if(result)
       return result;
 
-    if(!input_token_len)
+    if(!input_token_len) {
+      infof(conn->data,
+            "Negotiate handshake failure (empty challenge message)\n");
+
       return CURLE_BAD_CONTENT_ENCODING;
+    }
   }
 
   /* Setup the "output" security buffer */