diff --git a/packages/python/plotly/_plotly_utils/basevalidators.py b/packages/python/plotly/_plotly_utils/basevalidators.py
index 954ee39e659..099c26598c2 100644
--- a/packages/python/plotly/_plotly_utils/basevalidators.py
+++ b/packages/python/plotly/_plotly_utils/basevalidators.py
@@ -477,7 +477,9 @@ def build_regex_replacement(regex_str):
         #
         # To be cautious, we only perform this conversion for enumerated
         # values that match the anchor-style regex
-        match = re.match(r"\^(\w)\(\[2\-9\]\|\[1\-9\]\[0\-9\]\+\)\?\$", regex_str)
+        match = re.match(
+            r"\^(\w)\(\[2\-9\]\|\[1\-9\]\[0\-9\]\+\)\?\( domain\)\?\$", regex_str
+        )
 
         if match:
             anchor_char = match.group(1)
diff --git a/packages/python/plotly/optional-requirements.txt b/packages/python/plotly/optional-requirements.txt
index 450c32d3345..8ac97789fcf 100644
--- a/packages/python/plotly/optional-requirements.txt
+++ b/packages/python/plotly/optional-requirements.txt
@@ -25,7 +25,7 @@ psutil
 
 ## code formatting
 pre-commit
-black
+black==19.10b0
 
 ## codegen dependencies ##
 inflect