diff --git a/cunumeric/deferred.py b/cunumeric/deferred.py
index c887ac09b..7d575105f 100644
--- a/cunumeric/deferred.py
+++ b/cunumeric/deferred.py
@@ -391,6 +391,7 @@ def _zip_indices(self, start_index, arrays):
 
         # call ZIP function to combine index arrays into a singe array
         task = self.context.create_task(CuNumericOpCode.ZIP)
+        task.throws_exception(IndexError)
         task.add_output(output_arr.base)
         task.add_scalar_arg(self.ndim, ty.int64)  # N of points in Point<N>
         task.add_scalar_arg(key_dim, ty.int64)  # key_dim
diff --git a/src/cunumeric/index/zip.h b/src/cunumeric/index/zip.h
index 4cd5f1b4d..61a87104c 100644
--- a/src/cunumeric/index/zip.h
+++ b/src/cunumeric/index/zip.h
@@ -43,9 +43,12 @@ class ZipTask : public CuNumericTask<ZipTask> {
 #endif
 };
 
-constexpr coord_t compute_idx(coord_t index, coord_t dim)
+constexpr coord_t compute_idx(coord_t index, coord_t extent)
 {
-  return index < 0 ? index + dim : index;
+  coord_t new_index = index < 0 ? index + extent : index;
+  if (new_index < 0 || new_index >= extent)
+    throw legate::TaskException("index is out of bounds in index array");
+  return new_index;
 }
 
 }  // namespace cunumeric