This has been discussed in a couple of different bug reported
upstream:

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=486250
http://bugs.sourcemage.org/show_bug.cgi?id=14446

Fix:
http://lists.gnupg.org/pipermail/gnupg-devel/2008-April/024344.html

Upstream-Status: Backport [Debian]

Signed-off-by: Saul Wold <sgw@linux.intel.com>

Index: gnupg-1.4.7/keyserver/gpgkeys_curl.c
===================================================================
--- gnupg-1.4.7.orig/keyserver/gpgkeys_curl.c
+++ gnupg-1.4.7/keyserver/gpgkeys_curl.c
@@ -286,7 +286,7 @@ main(int argc,char *argv[])
       curl_easy_setopt(curl,CURLOPT_VERBOSE,1);
     }
 
-  curl_easy_setopt(curl,CURLOPT_SSL_VERIFYPEER,opt->flags.check_cert);
+  curl_easy_setopt(curl,CURLOPT_SSL_VERIFYPEER,(long)opt->flags.check_cert);
   curl_easy_setopt(curl,CURLOPT_CAINFO,opt->ca_cert_file);
 
   if(proxy)