diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6240fa8..8b9e6e7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,12 @@ All notable changes, updates, and fixes to pod5 will be documented here
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.3.6]
+
+## Fixed
+
+- Polars `ColumnNotFoundError: not_set` introduced by `polars==0.20.0`
+
 ## [0.3.5]
 
 ## Fixed
diff --git a/docs/requirements.txt b/docs/requirements.txt
index e0045f4..b2b0a58 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -2,4 +2,4 @@ sphinx-rtd-theme
 sphinx==v5.3.0
 myst-parser
 # Paths are relative to project root for ReadTheDocs and docs/Makefile
-pod5==0.3.5
+pod5==0.3.6
diff --git a/python/pod5/pyproject.toml b/python/pod5/pyproject.toml
index 0a300b6..a26696f 100644
--- a/python/pod5/pyproject.toml
+++ b/python/pod5/pyproject.toml
@@ -22,7 +22,7 @@ classifiers=[
 ]
 
 dependencies = [
-    "lib_pod5 == 0.3.5",
+    "lib_pod5 == 0.3.6",
     "iso8601",
     'importlib-metadata; python_version<"3.8"',
     "more_itertools",
diff --git a/python/pod5/src/pod5/tools/polars_utils.py b/python/pod5/src/pod5/tools/polars_utils.py
index 89f782d..2632809 100644
--- a/python/pod5/src/pod5/tools/polars_utils.py
+++ b/python/pod5/src/pod5/tools/polars_utils.py
@@ -23,4 +23,4 @@ def pl_format_read_id(read_id_col: pl.Expr) -> pl.Expr:
 
 def pl_format_empty_string(expr: pl.Expr, subst: Optional[str]) -> pl.Expr:
     """Empty strings are read as a pair of double-quotes which need to be removed"""
-    return pl.when(expr.str.lengths() == 0).then(subst).otherwise(expr)
+    return pl.when(expr.str.lengths() == 0).then(pl.lit(subst)).otherwise(expr)