diff --git a/docs/libcurl/libcurl.m4 b/docs/libcurl/libcurl.m4
index 01a0575cc531948433db664e05eb835cb49564ee..8cada0523a739ed994188949e6166d69d3eb91a3 100644
--- a/docs/libcurl/libcurl.m4
+++ b/docs/libcurl/libcurl.m4
@@ -157,6 +157,7 @@ x=CURLOPT_FILE;
 x=CURLOPT_ERRORBUFFER;
 x=CURLOPT_STDERR;
 x=CURLOPT_VERBOSE;
+if (x) ;
 ])],libcurl_cv_lib_curl_usable=yes,libcurl_cv_lib_curl_usable=no)
 
            CPPFLAGS=$_libcurl_save_cppflags