diff --git a/pyproject.toml b/pyproject.toml
index 1b2ee4a..fff593d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -3,7 +3,7 @@
 
 [build-system]
 requires = [
-  "setuptools == 75.6.0",
+  "setuptools == 75.8.0",
   "setuptools_scm[toml] == 8.1.0",
   "frequenz-repo-config[lib] == 0.11.0",
 ]
@@ -45,7 +45,7 @@ dev-flake8 = [
   "flake8 == 7.1.1",
   "flake8-docstrings == 1.7.0",
   "flake8-pyproject == 1.2.3",  # For reading the flake8 config from pyproject.toml
-  "pydoclint == 0.5.14",
+  "pydoclint == 0.6.0",
   "pydocstyle == 6.3.0",
 ]
 dev-formatting = ["black == 24.10.0", "isort == 5.13.2"]
@@ -56,7 +56,7 @@ dev-mkdocs = [
   "mkdocs-gen-files == 0.5.0",
   "mkdocs-literate-nav == 0.6.1",
   "mkdocs-macros-plugin == 1.3.7",
-  "mkdocs-material == 9.5.49",
+  "mkdocs-material == 9.6.1",
   "mkdocstrings[python] == 0.27.0",
   "mkdocstrings-python == 1.13.0",
   "frequenz-repo-config[lib] == 0.11.0",
@@ -75,12 +75,12 @@ dev-pylint = [
 ]
 dev-pytest = [
   "pytest == 8.3.4",
-  "pylint == 3.3.3",                                     # We need this to check for the examples
+  "pylint == 3.3.4",                                     # We need this to check for the examples
   "frequenz-repo-config[extra-lint-examples] == 0.11.0",
   "pytest-mock == 3.14.0",
-  "pytest-asyncio == 0.25.1",
+  "pytest-asyncio == 0.25.3",
   "async-solipsism == 0.7",
-  "hypothesis == 6.123.2",
+  "hypothesis == 6.124.9",
   "frequenz-quantities[marshmallow]",
 ]
 
diff --git a/src/frequenz/quantities/experimental/marshmallow.py b/src/frequenz/quantities/experimental/marshmallow.py
index ed0dc74..483bbdf 100644
--- a/src/frequenz/quantities/experimental/marshmallow.py
+++ b/src/frequenz/quantities/experimental/marshmallow.py
@@ -69,10 +69,12 @@ def _serialize(
         assert self.parent is not None
 
         # Determine the serialization format
-        serialize_as_string = self.metadata.get(
-            "serialize_as_string",
-            self.parent.context.get("serialize_as_string_default", False),
+        default = (
+            False
+            if self.parent.context is None
+            else self.parent.context.get("serialize_as_string_default", False)
         )
+        serialize_as_string = self.metadata.get("serialize_as_string", default)
 
         if serialize_as_string:
             # Use the Quantity's native string representation (includes unit)