diff --git a/lib/http.c b/lib/http.c
index ca9978042..a81a7bbf6 100644
--- a/lib/http.c
+++ b/lib/http.c
@@ -1620,11 +1620,11 @@ CURLcode Curl_http(struct connectdata *conn)
           if(!conn->bits.upload_chunky)
             /* We're not sending it 'chunked', append it to the request
                already now to reduce the number if send() calls */
-            add_buffer(req_buffer, data->set.postfields, postsize);
+            add_buffer(req_buffer, data->set.postfields, (size_t)postsize);
           else {
             /* Append the POST data chunky-style */
             add_bufferf(req_buffer, "%x\r\n", postsize);
-            add_buffer(req_buffer, data->set.postfields, postsize);
+            add_buffer(req_buffer, data->set.postfields, (size_t)postsize);
             add_buffer(req_buffer, "\r\n0\r\n\r\n", 7); /* end of a chunked
                                                            transfer stream */
           }
diff --git a/lib/urldata.h b/lib/urldata.h
index 1338c666e..05c8d6ce7 100644
--- a/lib/urldata.h
+++ b/lib/urldata.h
@@ -205,7 +205,7 @@ struct negotiatedata {
  ***************************************************************************/
 struct HTTP {
   struct FormData *sendit;
-  size_t postsize;
+  curl_off_t postsize; /* off_t to handle large file sizes */
   char *postdata;
 
   const char *p_pragma;      /* Pragma: string */
@@ -221,7 +221,7 @@ struct HTTP {
     curl_read_callback fread; /* backup storage for fread pointer */
     void *fread_in;           /* backup storage for fread_in pointer */
     char *postdata;
-    size_t postsize;
+    curl_off_t postsize;
   } backup;
 
   enum {