diff --git a/docs/examples/imap-append.c b/docs/examples/imap-append.c
index 3f832897d..bbf9fe436 100644
--- a/docs/examples/imap-append.c
+++ b/docs/examples/imap-append.c
@@ -85,6 +85,8 @@ int main(void)
 {
   CURL *curl;
   CURLcode res = CURLE_OK;
+  const char **p;
+  long infilesize;
   struct upload_status upload_ctx;
 
   upload_ctx.lines_read = 0;
@@ -107,6 +109,12 @@ int main(void)
     curl_easy_setopt(curl, CURLOPT_READDATA, &upload_ctx);
     curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);
 
+    infilesize = 0;
+    for(p = payload_text; *p; ++p) {
+      infilesize += (long)strlen(*p);
+    }
+    curl_easy_setopt(curl, CURLOPT_INFILESIZE, infilesize);
+
     /* Perform the append */
     res = curl_easy_perform(curl);