diff --git a/python/ray/rllib/utils/debug.py b/python/ray/rllib/utils/debug.py
index 0f636b0f0..2903d83c6 100644
--- a/python/ray/rllib/utils/debug.py
+++ b/python/ray/rllib/utils/debug.py
@@ -78,7 +78,10 @@ def _summarize(obj):
     elif isinstance(obj, tuple):
         return tuple(_summarize(x) for x in obj)
     elif isinstance(obj, np.ndarray):
-        if obj.dtype == np.object:
+        if obj.size == 0:
+            return _StringValue("np.ndarray({}, dtype={})".format(
+                obj.shape, obj.dtype))
+        elif obj.dtype == np.object:
             return _StringValue("np.ndarray({}, dtype={}, head={})".format(
                 obj.shape, obj.dtype, _summarize(obj[0])))
         else:
diff --git a/python/ray/rllib/utils/memory.py b/python/ray/rllib/utils/memory.py
index a51a18402..78bab8380 100644
--- a/python/ray/rllib/utils/memory.py
+++ b/python/ray/rllib/utils/memory.py
@@ -56,7 +56,11 @@ def aligned_array(size, dtype, align=64):
     empty = np.empty(n + (align - 1), dtype=np.uint8)
     data_align = empty.ctypes.data % align
     offset = 0 if data_align == 0 else (align - data_align)
-    output = empty[offset:offset + n].view(dtype)
+    if n == 0:
+        # stop np from optimising out empty slice reference
+        output = empty[offset:offset + 1][0:0].view(dtype)
+    else:
+        output = empty[offset:offset + n].view(dtype)
 
     assert len(output) == size, len(output)
     assert output.ctypes.data % align == 0, output.ctypes.data