diff --git a/Lib/ctypes/test/test_pep3118.py b/Lib/ctypes/test/test_pep3118.py
index 42a124e..9a830e9 100644
--- a/Lib/ctypes/test/test_pep3118.py
+++ b/Lib/ctypes/test/test_pep3118.py
@@ -12,6 +12,8 @@
 def normalize(format):
     # Remove current endian specifier and white space from a format
     # string
+    if format is None:
+        return ""
     format = format.replace(OTHER_ENDIAN, THIS_ENDIAN)
     return re.sub(r"\s", "", format)
 
@@ -84,6 +86,14 @@
 class aUnion(Union):
     _fields_ = [("a", c_int)]
 
+class Incomplete(Structure):
+    pass
+
+class Complete(Structure):
+    pass
+PComplete = POINTER(Complete)
+Complete._fields_ = [("a", c_int)]
+
 ################################################################
 #
 # This table contains format strings as they look on little endian
@@ -141,6 +151,16 @@
     # the pep does't support unions
     (aUnion,                    "B",                    None,           aUnion),
 
+    ## pointer to incomplete structure
+    (Incomplete,                "B",                    None,           Incomplete),
+    (POINTER(Incomplete),       "&B",                   None,           POINTER(Incomplete)),
+
+    # 'Complete' is a structure that starts incomplete, but is completed after the
+    # pointer type to it has been created.
+    (Complete,                  "T{<l:a:}",             None,           Complete),
+    # Unfortunately the pointer format string is not fixed...
+    (POINTER(Complete),         "&B",                   None,           POINTER(Complete)),
+
     ## other
 
     # function signatures are not implemented
diff --git a/Misc/NEWS b/Misc/NEWS
index a6ecc0e..010c06f 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -27,6 +27,9 @@
 Library
 -------
 
+- Issue #3258: Fixed a crash when a ctypes POINTER type to an
+  incomplete structure was created.
+
 - Issue #2683: Fix inconsistency in subprocess.Popen.communicate(): the
   argument now must be a bytes object in any case.
 
diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index c4ca29a..48fe772 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -353,6 +353,11 @@
 	}
 	Py_DECREF(result->tp_dict);
 	result->tp_dict = (PyObject *)dict;
+	dict->format = alloc_format_string(NULL, "B");
+	if (dict->format == NULL) {
+		Py_DECREF(result);
+		return NULL;
+	}
 
 	dict->paramfunc = StructUnionType_paramfunc;
 
@@ -871,7 +876,13 @@
 	if (proto) {
 		StgDictObject *itemdict = PyType_stgdict(proto);
 		assert(itemdict);
-		stgdict->format = alloc_format_string("&", itemdict->format);
+		/* If itemdict->format is NULL, then this is a pointer to an
+		   incomplete type.  We create a generic format string
+		   'pointer to bytes' in this case.  XXX Better would be to
+		   fix the format string later...
+		*/
+		stgdict->format = alloc_format_string("&",
+			      itemdict->format ? itemdict->format : "B");
 		if (stgdict->format == NULL) {
 			Py_DECREF((PyObject *)stgdict);
 			return NULL;