diff --git a/Misc/NEWS b/Misc/NEWS
index 3894d2e3683..3c9f382fe3f 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -175,6 +175,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #16628: Fix a memory leak in ctypes.resize().
+
 - Issue #13120: Allow to call pdb.set_trace() from thread.
   Patch by Ilya Sandler.
 
diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index 8be5958b0a0..603b3b8d8cf 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -2442,7 +2442,7 @@ PyCData_clear(CDataObject *self)
     assert(dict); /* Cannot be NULL for CDataObject instances */
     Py_CLEAR(self->b_objects);
     if ((self->b_needsfree)
-        && ((size_t)dict->size > sizeof(self->b_value)))
+        && _CDataObject_HasExternalBuffer(self))
         PyMem_Free(self->b_ptr);
     self->b_ptr = NULL;
     Py_CLEAR(self->b_base);
diff --git a/Modules/_ctypes/callproc.c b/Modules/_ctypes/callproc.c
index 1f3c1c01853..34659958a8b 100644
--- a/Modules/_ctypes/callproc.c
+++ b/Modules/_ctypes/callproc.c
@@ -1666,7 +1666,7 @@ resize(PyObject *self, PyObject *args)
         obj->b_size = size;
         goto done;
     }
-    if (obj->b_size <= sizeof(obj->b_value)) {
+    if (!_CDataObject_HasExternalBuffer(obj)) {
         /* We are currently using the objects default buffer, but it
            isn't large enough any more. */
         void *ptr = PyMem_Malloc(size);
diff --git a/Modules/_ctypes/ctypes.h b/Modules/_ctypes/ctypes.h
index 27abe65145f..5237ac23d6d 100644
--- a/Modules/_ctypes/ctypes.h
+++ b/Modules/_ctypes/ctypes.h
@@ -116,6 +116,7 @@ extern int PyObject_stginfo(PyObject *self, Py_ssize_t *psize, Py_ssize_t *palig
 extern PyTypeObject PyCData_Type;
 #define CDataObject_CheckExact(v)       ((v)->ob_type == &PyCData_Type)
 #define CDataObject_Check(v)            PyObject_TypeCheck(v, &PyCData_Type)
+#define _CDataObject_HasExternalBuffer(v)  ((v)->b_ptr != (char *)&(v)->b_value)
 
 extern PyTypeObject PyCSimpleType_Type;
 #define PyCSimpleTypeObject_CheckExact(v)       ((v)->ob_type == &PyCSimpleType_Type)