diff --git a/setup.py b/setup.py
index 65110e8..14cf623 100644
--- a/setup.py
+++ b/setup.py
@@ -41,6 +41,11 @@ requires = [
     #
     # package                           # low                   high
 
+    # TODO: v1.1 suddenly caused an issue; perhaps can remove this
+    # restriction once a later version comes out?
+    # cf. https://docs.pylonsproject.org/projects/plaster/en/latest/changes.html
+    'plaster<1.1',                      # 1.0
+
     # TODO: can remove this once tailbone requires it
     'pyramid_retry',                    # 1.0