diff --git a/http.c b/http.c
index 8be75b267f..82664ddddb 100644
--- a/http.c
+++ b/http.c
@@ -867,6 +867,9 @@ static CURL *get_curl_handle(void)
 			strbuf_release(&url);
 		}
 
+		if (!proxy_auth.host)
+			die("Invalid proxy URL '%s'", curl_http_proxy);
+
 		curl_easy_setopt(result, CURLOPT_PROXY, proxy_auth.host);
 #if LIBCURL_VERSION_NUM >= 0x071304
 		var_override(&curl_no_proxy, getenv("NO_PROXY"));