diff --git a/message_ix_models/report/util.py b/message_ix_models/report/util.py
index f4d13542f4..0b5c8b9275 100644
--- a/message_ix_models/report/util.py
+++ b/message_ix_models/report/util.py
@@ -5,6 +5,7 @@
 from dask.core import quote
 from genno import Quantity
 from genno.compat.pyam.util import collapse as genno_collapse
+from genno.core.key import single_key
 from iam_units import registry
 from message_ix.reporting import Key, Reporter
 from sdmx.model.v21 import Code
@@ -191,7 +192,7 @@ def copy_ts(rep: Reporter, other: str, filters: Optional[dict]) -> Key:
 
     k1 = rep.add("from_url", f"scenario {_id}", quote(other))
     k2 = rep.add("get_ts", f"ts data {_id}", k1, filters)
-    return rep.add("store_ts", f"copy ts {_id}", "scenario", k2)
+    return single_key(rep.add("store_ts", f"copy ts {_id}", "scenario", k2))
 
 
 def add_replacements(dim: str, codes: Iterable[Code]) -> None:
diff --git a/message_ix_models/workflow.py b/message_ix_models/workflow.py
index d9d303088f..55b6e02e17 100644
--- a/message_ix_models/workflow.py
+++ b/message_ix_models/workflow.py
@@ -191,7 +191,7 @@ def add_step(
             self.graph.pop(name, None)
 
         # Add to the Computer; return the name of the added step
-        return self.add_single(name, step, "context", base, strict=True)
+        return str(self.add_single(name, step, "context", base, strict=True))
 
     def run(self, name_or_names: Union[str, List[str]]):
         """Run all workflow steps necessary to produce `name_or_names`.
diff --git a/pyproject.toml b/pyproject.toml
index eefff7b84f..a1e7b12032 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -5,12 +5,10 @@ requires = ["build", "setuptools-scm"]
 dynamic = ["version"]
 name = "message-ix-models"
 description = "Tools for the MESSAGEix-GLOBIOM family of models"
-authors = [
-  {name = "IIASA Energy, Climate, and Environment (ECE) Program"},
-]
+authors = [{ name = "IIASA Energy, Climate, and Environment (ECE) Program" }]
 maintainers = [
-  {name = "Paul Natsuo Kishimoto", email = "mail@paul.kishimoto.name"},
-  {name = "Fridolin Glatter", email = "glatter@iiasa.ac.at"},
+  { name = "Paul Natsuo Kishimoto", email = "mail@paul.kishimoto.name" },
+  { name = "Fridolin Glatter", email = "glatter@iiasa.ac.at" },
 ]
 readme = "README.rst"
 classifiers = [
@@ -28,7 +26,7 @@ classifiers = [
   "Programming Language :: Python :: 3.11",
   "Programming Language :: R",
   "Topic :: Scientific/Engineering",
-  "Topic :: Scientific/Engineering :: Information Analysis"
+  "Topic :: Scientific/Engineering :: Information Analysis",
 ]
 requires-python = ">=3.8"
 dependencies = [
@@ -36,7 +34,7 @@ dependencies = [
   "colorama",
   # When the minimum is greater than the minimum via message_ix; e.g.
   # message_ix >= 3.4.0 → ixmp >= 3.4.0 → genno >= 1.6.0",
-  "genno >= 1.8.0",
+  "genno >= 1.18.0",
   "iam_units",
   "message_ix >= 3.4.0",
   "pooch",