diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0ddfce9afe27ec..d2c97cfe1b74ec 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1183,6 +1183,8 @@ check_type_size("off_t"  SIZEOF_OFF_T)
 set(CMAKE_REQUIRED_INCLUDES "${CURL_SOURCE_DIR}/include")
 set(CMAKE_EXTRA_INCLUDE_FILES "curl/system.h")
 check_type_size("curl_off_t"  SIZEOF_CURL_OFF_T)
+set(CMAKE_EXTRA_INCLUDE_FILES "curl/curl.h")
+check_type_size("curl_socket_t"  SIZEOF_CURL_SOCKET_T)
 set(CMAKE_EXTRA_INCLUDE_FILES "")
 
 if(WIN32)
diff --git a/configure.ac b/configure.ac
index 8a8eb0e547c301..e351d1e184d1ca 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3477,6 +3477,9 @@ CPPFLAGS="-I$srcdir/include $CPPFLAGS"
 CURL_SIZEOF(curl_off_t, [
 #include <curl/system.h>
 ])
+CURL_SIZEOF(curl_socket_t, [
+#include <curl/curl.h>
+])
 CPPFLAGS=$o
 
 AC_CHECK_TYPE(long long,
diff --git a/lib/cf-socket.c b/lib/cf-socket.c
index 6d9ace42612183..523560fedc1dbe 100644
--- a/lib/cf-socket.c
+++ b/lib/cf-socket.c
@@ -786,14 +786,14 @@ static void cf_socket_close(struct Curl_cfilter *cf, struct Curl_easy *data)
        * closed it) and we just forget about it.
        */
       if(ctx->sock == cf->conn->sock[cf->sockindex]) {
-        DEBUGF(LOG_CF(data, cf, "cf_socket_close(%d, active)",
-                     (int)ctx->sock));
+        DEBUGF(LOG_CF(data, cf, "cf_socket_close(%" CURL_FORMAT_SOCKET_T
+                      ", active)", ctx->sock));
         socket_close(data, cf->conn, !ctx->accepted, ctx->sock);
         cf->conn->sock[cf->sockindex] = CURL_SOCKET_BAD;
       }
       else {
-        DEBUGF(LOG_CF(data, cf, "cf_socket_close(%d) no longer at "
-                      "conn->sock[], discarding", (int)ctx->sock));
+        DEBUGF(LOG_CF(data, cf, "cf_socket_close(%" CURL_FORMAT_SOCKET_T
+                      ") no longer at conn->sock[], discarding", ctx->sock));
         /* TODO: we do not want this to happen. Need to check which
          * code is messing with conn->sock[cf->sockindex] */
       }
@@ -803,8 +803,8 @@ static void cf_socket_close(struct Curl_cfilter *cf, struct Curl_easy *data)
     }
     else {
       /* this is our local socket, we did never publish it */
-      DEBUGF(LOG_CF(data, cf, "cf_socket_close(%d, not active)",
-                    (int)ctx->sock));
+      DEBUGF(LOG_CF(data, cf, "cf_socket_close(%" CURL_FORMAT_SOCKET_T
+                    ", not active)", ctx->sock));
       sclose(ctx->sock);
       ctx->sock = CURL_SOCKET_BAD;
     }
@@ -975,7 +975,8 @@ static CURLcode cf_socket_open(struct Curl_cfilter *cf,
     ctx->connected_at = Curl_now();
     cf->connected = TRUE;
   }
-  DEBUGF(LOG_CF(data, cf, "cf_socket_open() -> %d, fd=%d", result, ctx->sock));
+  DEBUGF(LOG_CF(data, cf, "cf_socket_open() -> %d, fd=%" CURL_FORMAT_SOCKET_T,
+                result, ctx->sock));
   return result;
 }
 
@@ -1016,7 +1017,8 @@ static int do_connect(struct Curl_cfilter *cf, struct Curl_easy *data,
 #elif defined(TCP_FASTOPEN_CONNECT) /* Linux >= 4.11 */
     if(setsockopt(ctx->sock, IPPROTO_TCP, TCP_FASTOPEN_CONNECT,
                   (void *)&optval, sizeof(optval)) < 0)
-      infof(data, "Failed to enable TCP Fast Open on fd %d", ctx->sock);
+      infof(data, "Failed to enable TCP Fast Open on fd %"
+            CURL_FORMAT_SOCKET_T, ctx->sock);
 
     rc = connect(ctx->sock, &ctx->addr.sa_addr, ctx->addr.addrlen);
 #elif defined(MSG_FASTOPEN) /* old Linux */
@@ -1580,9 +1582,10 @@ static CURLcode cf_udp_setup_quic(struct Curl_cfilter *cf,
     return Curl_socket_connect_result(data, ctx->r_ip, SOCKERRNO);
   }
   set_local_ip(cf, data);
-  DEBUGF(LOG_CF(data, cf, "%s socket %d connected: [%s:%d] -> [%s:%d]",
-         (ctx->transport == TRNSPRT_QUIC)? "QUIC" : "UDP",
-         ctx->sock, ctx->l_ip, ctx->l_port, ctx->r_ip, ctx->r_port));
+  DEBUGF(LOG_CF(data, cf, "%s socket %" CURL_FORMAT_SOCKET_T
+                " connected: [%s:%d] -> [%s:%d]",
+                (ctx->transport == TRNSPRT_QUIC)? "QUIC" : "UDP",
+                ctx->sock, ctx->l_ip, ctx->l_port, ctx->r_ip, ctx->r_port));
 
   (void)curlx_nonblock(ctx->sock, TRUE);
   switch(ctx->addr.family) {
@@ -1634,12 +1637,13 @@ static CURLcode cf_udp_connect(struct Curl_cfilter *cf,
       result = cf_udp_setup_quic(cf, data);
       if(result)
         goto out;
-      DEBUGF(LOG_CF(data, cf, "cf_udp_connect(), opened socket=%d (%s:%d)",
+      DEBUGF(LOG_CF(data, cf, "cf_udp_connect(), opened socket=%"
+                    CURL_FORMAT_SOCKET_T " (%s:%d)",
                     ctx->sock, ctx->l_ip, ctx->l_port));
     }
     else {
-      DEBUGF(LOG_CF(data, cf, "cf_udp_connect(), opened socket=%d "
-                    "(unconnected)", ctx->sock));
+      DEBUGF(LOG_CF(data, cf, "cf_udp_connect(), opened socket=%"
+                    CURL_FORMAT_SOCKET_T " (unconnected)", ctx->sock));
     }
     *done = TRUE;
     cf->connected = TRUE;
@@ -1811,7 +1815,8 @@ CURLcode Curl_conn_tcp_listen_set(struct Curl_easy *data,
   ctx->active = TRUE;
   ctx->connected_at = Curl_now();
   cf->connected = TRUE;
-  DEBUGF(LOG_CF(data, cf, "Curl_conn_tcp_listen_set(%d)", (int)ctx->sock));
+  DEBUGF(LOG_CF(data, cf, "Curl_conn_tcp_listen_set(%"
+                CURL_FORMAT_SOCKET_T ")", ctx->sock));
 
 out:
   if(result) {
@@ -1875,8 +1880,9 @@ CURLcode Curl_conn_tcp_accepted_set(struct Curl_easy *data,
   ctx->accepted = TRUE;
   ctx->connected_at = Curl_now();
   cf->connected = TRUE;
-  DEBUGF(LOG_CF(data, cf, "accepted_set(sock=%d, remote=%s port=%d)",
-         (int)ctx->sock, ctx->r_ip, ctx->r_port));
+  DEBUGF(LOG_CF(data, cf, "accepted_set(sock=%" CURL_FORMAT_SOCKET_T
+                ", remote=%s port=%d)",
+                ctx->sock, ctx->r_ip, ctx->r_port));
 
   return CURLE_OK;
 }
diff --git a/lib/cf-socket.h b/lib/cf-socket.h
index 0eec61adb74781..652cb5fa24390b 100644
--- a/lib/cf-socket.h
+++ b/lib/cf-socket.h
@@ -34,6 +34,23 @@ struct Curl_easy;
 struct connectdata;
 struct Curl_sockaddr_ex;
 
+#ifndef SIZEOF_CURL_SOCKET_T
+/* configure and cmake check and set the define */
+# ifdef _WIN64
+#  define SIZEOF_CURL_SOCKET_T 8
+# else
+/* default guess */
+#  define SIZEOF_CURL_SOCKET_T 4
+# endif
+#endif
+
+#if SIZEOF_CURL_SOCKET_T < 8
+# define CURL_FORMAT_SOCKET_T "d"
+#else
+# define CURL_FORMAT_SOCKET_T "qd"
+#endif
+
+
 /*
  * The Curl_sockaddr_ex structure is basically libcurl's external API
  * curl_sockaddr structure with enough space available to directly hold any
diff --git a/lib/connect.c b/lib/connect.c
index 10d0c11ae990ec..2dd4e66f24d56c 100644
--- a/lib/connect.c
+++ b/lib/connect.c
@@ -663,7 +663,8 @@ static CURLcode is_connected(struct Curl_cfilter *cf,
           DEBUGF(LOG_CF(data, cf, "%s done", baller->name));
         }
         else {
-          DEBUGF(LOG_CF(data, cf, "%s starting (timeout=%ldms)",
+          DEBUGF(LOG_CF(data, cf, "%s starting (timeout=%"
+                        CURL_FORMAT_TIMEDIFF_T "ms)",
                         baller->name, baller->timeoutms));
           ++ongoing;
           ++added;
@@ -801,7 +802,8 @@ static CURLcode start_connect(struct Curl_cfilter *cf,
                           timeout_ms,  EXPIRE_DNS_PER_NAME);
   if(result)
     return result;
-  DEBUGF(LOG_CF(data, cf, "created %s (timeout %ldms)",
+  DEBUGF(LOG_CF(data, cf, "created %s (timeout %"
+                CURL_FORMAT_TIMEDIFF_T "ms)",
                 ctx->baller[0]->name, ctx->baller[0]->timeoutms));
   if(addr1) {
     /* second one gets a delayed start */
@@ -812,7 +814,8 @@ static CURLcode start_connect(struct Curl_cfilter *cf,
                             timeout_ms,  EXPIRE_DNS_PER_NAME2);
     if(result)
       return result;
-    DEBUGF(LOG_CF(data, cf, "created %s (timeout %ldms)",
+    DEBUGF(LOG_CF(data, cf, "created %s (timeout %"
+                  CURL_FORMAT_TIMEDIFF_T "ms)",
                   ctx->baller[1]->name, ctx->baller[1]->timeoutms));
   }