diff --git a/Modules/_ctypes/callproc.c b/Modules/_ctypes/callproc.c
index a084f812f60..ba0e0fcb51e 100644
--- a/Modules/_ctypes/callproc.c
+++ b/Modules/_ctypes/callproc.c
@@ -82,6 +82,10 @@
 #define DONT_USE_SEH
 #endif
 
+#ifndef PY_FORMAT_SIZE_T 
+#define PY_FORMAT_SIZE_T ""
+#endif
+
 #ifdef MS_WIN32
 PyObject *ComError;
 
@@ -1486,7 +1490,8 @@ resize(PyObject *self, PyObject *args)
 	}
 	if (size < dict->size) {
 		PyErr_Format(PyExc_ValueError,
-			     "minimum size is %d", dict->size);
+			     "minimum size is %" PY_FORMAT_SIZE_T "d",
+			     dict->size);
 		return NULL;
 	}
 	if (obj->b_needsfree == 0) {