diff --git a/Misc/NEWS b/Misc/NEWS
index 44a893ff0ec..185e5cf4c79 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -163,6 +163,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #5203: Fixed ctypes segfaults when passing a unicode string to a
+  function without argtypes (only occurs if HAVE_USABLE_WCHAR_T is false).
+
 - Issue #3386: distutils.sysconfig.get_python_lib prefix argument was ignored
   under NT and OS2. Patch by Philip Jenvey.
 
diff --git a/Modules/_ctypes/callproc.c b/Modules/_ctypes/callproc.c
index 3bd6d664ef5..c153ae2c196 100644
--- a/Modules/_ctypes/callproc.c
+++ b/Modules/_ctypes/callproc.c
@@ -645,14 +645,15 @@ static int ConvParam(PyObject *obj, Py_ssize_t index, struct argument *pa)
 
 #ifdef CTYPES_UNICODE
 	if (PyUnicode_Check(obj)) {
-		pa->ffi_type = &ffi_type_pointer;
 #ifdef HAVE_USABLE_WCHAR_T
+		pa->ffi_type = &ffi_type_pointer;
 		pa->value.p = PyUnicode_AS_UNICODE(obj);
 		Py_INCREF(obj);
 		pa->keep = obj;
 		return 0;
 #else
 		int size = PyUnicode_GET_SIZE(obj);
+		pa->ffi_type = &ffi_type_pointer;
 		size += 1; /* terminating NUL */
 		size *= sizeof(wchar_t);
 		pa->value.p = PyMem_Malloc(size);