diff --git a/src/httpfs_curl_client.cpp b/src/httpfs_curl_client.cpp
index d4e39bf..f90d04f 100644
--- a/src/httpfs_curl_client.cpp
+++ b/src/httpfs_curl_client.cpp
@@ -168,7 +168,7 @@ class HTTPFSCurlClient : public HTTPClient {
 
 		if (!http_params.http_proxy.empty()) {
 			curl_easy_setopt(*curl, CURLOPT_PROXY,
-			                 StringUtil::Format("%s:%s", http_params.http_proxy, http_params.http_proxy_port).c_str());
+			                 StringUtil::Format("%s:%d", http_params.http_proxy, http_params.http_proxy_port).c_str());
 
 			if (!http_params.http_proxy_username.empty()) {
 				curl_easy_setopt(*curl, CURLOPT_PROXYUSERNAME, http_params.http_proxy_username.c_str());