diff --git a/pymbolic/imperative/utils.py b/pymbolic/imperative/utils.py
index 6df33a69..5041ef1f 100644
--- a/pymbolic/imperative/utils.py
+++ b/pymbolic/imperative/utils.py
@@ -94,9 +94,9 @@ def get_node_attrs(stmt):
 
         if 0:
             for dep in stmt.then_depends_on:
-                annotation_dep_graph[(stmt.id, dep)] = "then"
+                annotation_dep_graph[stmt.id, dep] = "then"
             for dep in stmt.else_depends_on:
-                annotation_dep_graph[(stmt.id, dep)] = "else"
+                annotation_dep_graph[stmt.id, dep] = "else"
 
     # {{{ O(n^3) (i.e. slow) transitive reduction
 
diff --git a/pymbolic/mapper/__init__.py b/pymbolic/mapper/__init__.py
index 034cc755..56b34a82 100644
--- a/pymbolic/mapper/__init__.py
+++ b/pymbolic/mapper/__init__.py
@@ -1063,11 +1063,12 @@ def map_common_subexpression(self, expr, *args):
         except AttributeError:
             ccd = self._cse_cache_dict = {}
 
+        key = (expr, *args)
         try:
-            return ccd[(expr, *args)]
+            return ccd[key]
         except KeyError:
             result = self.map_common_subexpression_uncached(expr, *args)
-            ccd[(expr, *args)] = result
+            ccd[key] = result
             return result
 
     @abstractmethod
diff --git a/pyproject.toml b/pyproject.toml
index 3e4435dd..f416506d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -74,6 +74,7 @@ extend-select = [
     "W",    # pycodestyle
 ]
 extend-ignore = [
+    "C409", # remove comprehension within tuple call
     "C90",  # McCabe complexity
     "E226", # missing whitespace around arithmetic operator
     "E241", # multiple spaces after comma