diff --git a/lib/warnless.c b/lib/warnless.c
index 778f098f555204f596d5acfb872762a150b1c5fa..8c130d34c5e16af1089e95ac48a8f5911054c254 100644
--- a/lib/warnless.c
+++ b/lib/warnless.c
@@ -174,6 +174,25 @@ int curlx_ultosi(unsigned long ulnum)
 #endif
 }
 
+/*
+** unsigned size_t to signed curl_off_t
+*/
+
+curl_off_t curlx_uztoso(size_t uznum)
+{
+#ifdef __INTEL_COMPILER
+#  pragma warning(push)
+#  pragma warning(disable:810) /* conversion may lose significant bits */
+#endif
+
+  DEBUGASSERT(uznum <= (size_t) CURL_MASK_SCOFFT);
+  return (curl_off_t)(uznum & (size_t) CURL_MASK_SCOFFT);
+
+#ifdef __INTEL_COMPILER
+#  pragma warning(pop)
+#endif
+}
+
 /*
 ** unsigned size_t to signed int
 */
diff --git a/lib/warnless.h b/lib/warnless.h
index 33368d207c6924e274907c975156df14cebab50f..ad77d3c20bb13dbbc9845022110fb34285d6af74 100644
--- a/lib/warnless.h
+++ b/lib/warnless.h
@@ -34,6 +34,8 @@ int curlx_ultosi(unsigned long ulnum);
 
 int curlx_uztosi(size_t uznum);
 
+curl_off_t curlx_uztoso(size_t uznum);
+
 unsigned long curlx_uztoul(size_t uznum);
 
 unsigned int curlx_uztoui(size_t uznum);
diff --git a/src/tool_getparam.c b/src/tool_getparam.c
index 6d68c5b40f5469b9027f552eadb41752ac3ce076..9ac6ab2fc7e6fd4ec19af586539cb5632e5c7991 100644
--- a/src/tool_getparam.c
+++ b/src/tool_getparam.c
@@ -1239,7 +1239,7 @@ ParameterError getparameter(char *flag,    /* f or -long-flag */
            &-letter */
         char *oldpost = config->postfields;
         curl_off_t oldlen = config->postfieldsize;
-        curl_off_t newlen = oldlen + size + 2;
+        curl_off_t newlen = oldlen + curlx_uztoso(size) + 2;
         config->postfields = malloc((size_t)newlen);
         if(!config->postfields) {
           Curl_safefree(oldpost);
@@ -1257,7 +1257,7 @@ ParameterError getparameter(char *flag,    /* f or -long-flag */
       }
       else {
         config->postfields = postdata;
-        config->postfieldsize = size;
+        config->postfieldsize = curlx_uztoso(size);
       }
     }
     /*