diff --git a/lib/url.c b/lib/url.c
index ac496bb8d4eb82..d0c64281e73200 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -1397,8 +1397,15 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
      * Set HTTP Authentication type BITMASK.
      */
   {
+    int bitcheck;
+    bool authbits;
     unsigned long auth = va_arg(param, unsigned long);
 
+    if(auth == CURLAUTH_NONE) {
+      data->set.httpauth = auth;
+      break;
+    }
+
     /* the DIGEST_IE bit is only used to set a special marker, for all the
        rest we need to handle it as normal DIGEST */
     data->state.authhost.iestyle = (auth & CURLAUTH_DIGEST_IE)?TRUE:FALSE;
@@ -1419,7 +1426,17 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
     auth &= ~CURLAUTH_GSSNEGOTIATE; /* no GSS-Negotiate without GSSAPI or
                                        WINDOWS_SSPI */
 #endif
-    if(!auth)
+
+    /* check if any auth bit lower than CURLAUTH_ONLY is still set */
+    bitcheck = 0;
+    authbits = FALSE;
+    while(bitcheck < 31) {
+      if(auth & (1UL << bitcheck++)) {
+        authbits = TRUE;
+        break;
+      }
+    }
+    if(!authbits)
       return CURLE_NOT_BUILT_IN; /* no supported types left! */
 
     data->set.httpauth = auth;
@@ -1461,8 +1478,15 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
      * Set HTTP Authentication type BITMASK.
      */
   {
+    int bitcheck;
+    bool authbits;
     unsigned long auth = va_arg(param, unsigned long);
 
+    if(auth == CURLAUTH_NONE) {
+      data->set.proxyauth = auth;
+      break;
+    }
+
     /* the DIGEST_IE bit is only used to set a special marker, for all the
        rest we need to handle it as normal DIGEST */
     data->state.authproxy.iestyle = (auth & CURLAUTH_DIGEST_IE)?TRUE:FALSE;
@@ -1482,7 +1506,17 @@ CURLcode Curl_setopt(struct SessionHandle *data, CURLoption option,
     auth &= ~CURLAUTH_GSSNEGOTIATE; /* no GSS-Negotiate without GSSAPI or
                                        WINDOWS_SSPI */
 #endif
-    if(!auth)
+
+    /* check if any auth bit lower than CURLAUTH_ONLY is still set */
+    bitcheck = 0;
+    authbits = FALSE;
+    while(bitcheck < 31) {
+      if(auth & (1UL << bitcheck++)) {
+        authbits = TRUE;
+        break;
+      }
+    }
+    if(!authbits)
       return CURLE_NOT_BUILT_IN; /* no supported types left! */
 
     data->set.proxyauth = auth;