diff --git a/loopy/kernel/array.py b/loopy/kernel/array.py
index 85c905e3fe1898b9a81fa8c41cdac8d0a2bfc1b3..e829d70019a981958b4ecef85bd8aae489c7ca97 100644
--- a/loopy/kernel/array.py
+++ b/loopy/kernel/array.py
@@ -918,6 +918,11 @@ def get_access_info(ary, index, eval_expr):
     array_name = ary.name
 
     if ary.shape is None:
+        if len(index) != 1:
+            raise LoopyError("Array '%s' has unknown shape (shape is None) and "
+                    "therefore only supports one-dimensional indexing."
+                    % ary.name)
+
         return AccessInfo(array_name=array_name, subscripts=index, vector_index=None)
 
     if len(ary.shape) != len(index):