diff --git a/Lib/test/test_array.py b/Lib/test/test_array.py
index 8fd54cc1dbe..1f8967ccff3 100644
--- a/Lib/test/test_array.py
+++ b/Lib/test/test_array.py
@@ -36,14 +36,24 @@ typecodes = "ubBhHiIlLfd"
 if have_long_long:
     typecodes += 'qQ'
 
-class BadConstructorTest(unittest.TestCase):
+class MiscTest(unittest.TestCase):
 
-    def test_constructor(self):
+    def test_bad_constructor(self):
         self.assertRaises(TypeError, array.array)
         self.assertRaises(TypeError, array.array, spam=42)
         self.assertRaises(TypeError, array.array, 'xx')
         self.assertRaises(ValueError, array.array, 'x')
 
+    def test_empty(self):
+        # Exercise code for handling zero-length arrays
+        a = array.array('B')
+        a[:] = a
+        self.assertEqual(len(a), 0)
+        self.assertEqual(len(a + a), 0)
+        self.assertEqual(len(a * 3), 0)
+        a += a
+        self.assertEqual(len(a), 0)
+
 
 # Machine format codes.
 #
diff --git a/Misc/NEWS b/Misc/NEWS
index de45fc95ab6..9e6975e39d5 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -96,6 +96,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #27570: Avoid zero-length memcpy() etc calls with null source
+  pointers in the "ctypes" and "array" modules.
+
 - Issue #22233: Break email header lines *only* on the RFC specified CR and LF
   characters, not on arbitrary unicode line breaks.  This also fixes a bug in
   HTTP header parsing.
diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index f8407298fed..b3a95811eb4 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -1375,8 +1375,10 @@ PyCArrayType_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
         goto error;
     }
     stgdict->shape[0] = length;
-    memmove(&stgdict->shape[1], itemdict->shape,
-        sizeof(Py_ssize_t) * (stgdict->ndim - 1));
+    if (stgdict->ndim > 1) {
+        memmove(&stgdict->shape[1], itemdict->shape,
+            sizeof(Py_ssize_t) * (stgdict->ndim - 1));
+    }
 
     itemsize = itemdict->size;
     if (length * itemsize < 0) {
diff --git a/Modules/_ctypes/stgdict.c b/Modules/_ctypes/stgdict.c
index 879afb8424f..6c0fda901a6 100644
--- a/Modules/_ctypes/stgdict.c
+++ b/Modules/_ctypes/stgdict.c
@@ -391,9 +391,11 @@ PyCStructUnionType_update_stgdict(PyObject *type, PyObject *fields, int isStruct
         }
         memset(stgdict->ffi_type_pointer.elements, 0,
                sizeof(ffi_type *) * (basedict->length + len + 1));
-        memcpy(stgdict->ffi_type_pointer.elements,
-               basedict->ffi_type_pointer.elements,
-               sizeof(ffi_type *) * (basedict->length));
+        if (basedict->length > 0) {
+            memcpy(stgdict->ffi_type_pointer.elements,
+                   basedict->ffi_type_pointer.elements,
+                   sizeof(ffi_type *) * (basedict->length));
+        }
         ffi_ofs = basedict->length;
     } else {
         offset = 0;
diff --git a/Modules/arraymodule.c b/Modules/arraymodule.c
index 86a58d9170b..5868c52ca8a 100644
--- a/Modules/arraymodule.c
+++ b/Modules/arraymodule.c
@@ -740,8 +740,10 @@ array_slice(arrayobject *a, Py_ssize_t ilow, Py_ssize_t ihigh)
     np = (arrayobject *) newarrayobject(&Arraytype, ihigh - ilow, a->ob_descr);
     if (np == NULL)
         return NULL;
-    memcpy(np->ob_item, a->ob_item + ilow * a->ob_descr->itemsize,
-           (ihigh-ilow) * a->ob_descr->itemsize);
+    if (ihigh > ilow) {
+        memcpy(np->ob_item, a->ob_item + ilow * a->ob_descr->itemsize,
+               (ihigh-ilow) * a->ob_descr->itemsize);
+    }
     return (PyObject *)np;
 }
 
@@ -799,9 +801,13 @@ array_concat(arrayobject *a, PyObject *bb)
     if (np == NULL) {
         return NULL;
     }
-    memcpy(np->ob_item, a->ob_item, Py_SIZE(a)*a->ob_descr->itemsize);
-    memcpy(np->ob_item + Py_SIZE(a)*a->ob_descr->itemsize,
-           b->ob_item, Py_SIZE(b)*b->ob_descr->itemsize);
+    if (Py_SIZE(a) > 0) {
+        memcpy(np->ob_item, a->ob_item, Py_SIZE(a)*a->ob_descr->itemsize);
+    }
+    if (Py_SIZE(b) > 0) {
+        memcpy(np->ob_item + Py_SIZE(a)*a->ob_descr->itemsize,
+               b->ob_item, Py_SIZE(b)*b->ob_descr->itemsize);
+    }
     return (PyObject *)np;
 #undef b
 }
@@ -821,7 +827,7 @@ array_repeat(arrayobject *a, Py_ssize_t n)
     np = (arrayobject *) newarrayobject(&Arraytype, size, a->ob_descr);
     if (np == NULL)
         return NULL;
-    if (n == 0)
+    if (size == 0)
         return (PyObject *)np;
     oldbytes = Py_SIZE(a) * a->ob_descr->itemsize;
     newbytes = oldbytes * n;
@@ -942,8 +948,10 @@ array_do_extend(arrayobject *self, PyObject *bb)
     size = oldsize + Py_SIZE(b);
     if (array_resize(self, size) == -1)
         return -1;
-    memcpy(self->ob_item + oldsize * self->ob_descr->itemsize,
-        b->ob_item, bbsize * b->ob_descr->itemsize);
+    if (bbsize > 0) {
+        memcpy(self->ob_item + oldsize * self->ob_descr->itemsize,
+            b->ob_item, bbsize * b->ob_descr->itemsize);
+    }
 
     return 0;
 #undef b