diff --git a/Lib/multiprocessing/heap.py b/Lib/multiprocessing/heap.py
index 6217dfe12689b3..f1d74d245101c0 100644
--- a/Lib/multiprocessing/heap.py
+++ b/Lib/multiprocessing/heap.py
@@ -20,6 +20,12 @@
 
 __all__ = ['BufferWrapper']
 
+#
+# Module constants
+#
+
+_MAXSIZE = sys.maxsize
+
 #
 # Inheritable class which wraps an mmap, and from which blocks can be allocated
 #
@@ -108,6 +114,17 @@ def rebuild_arena(size, dupfd):
 
     reduction.register(Arena, reduce_arena)
 
+#
+# Validation helpers
+#
+
+def _validate_size(size):
+    """Validate requested size; raise ValueError if < 0, OverflowError if >= _MAXSIZE."""
+    if size < 0:
+        raise ValueError("Size {0:n} out of range".format(size))
+    if _MAXSIZE <= size:
+        raise OverflowError("Size {0:n} too large".format(size))
+
 #
 # Class allowing allocation of chunks of memory from arenas
 #
@@ -295,10 +312,7 @@ def free(self, block):
 
     def malloc(self, size):
         # return a block of right size (possibly rounded up)
-        if size < 0:
-            raise ValueError("Size {0:n} out of range".format(size))
-        if sys.maxsize <= size:
-            raise OverflowError("Size {0:n} too large".format(size))
+        _validate_size(size)
         if os.getpid() != self._lastpid:
             self.__init__()                     # reinitialize after fork
         with self._lock:
@@ -324,10 +338,7 @@ class BufferWrapper(object):
     _heap = Heap()
 
     def __init__(self, size):
-        if size < 0:
-            raise ValueError("Size {0:n} out of range".format(size))
-        if sys.maxsize <= size:
-            raise OverflowError("Size {0:n} too large".format(size))
+        _validate_size(size)
         block = BufferWrapper._heap.malloc(size)
         self._state = (block, size)
         util.Finalize(self, BufferWrapper._heap.free, args=(block,))