diff --git a/lisa/__init__.py b/lisa/__init__.py
index 2990da167d084bbe0ab5e6673db81bca8abd2eb3..ccb42e0379df1974cd8701645f9ddc102ae5d724 100644
--- a/lisa/__init__.py
+++ b/lisa/__init__.py
@@ -40,4 +40,8 @@ warnings.filterwarnings(
     module=r'__main__',
 )
 
+# Work around the warnings reported here:
+# https://github.com/pola-rs/polars/issues/20000
+os.environ.setdefault('POLARS_ALLOW_FORKING_THREAD', '1')
+
 # vim :set tabstop=4 shiftwidth=4 textwidth=80 expandtab
diff --git a/lisa/analysis/tasks.py b/lisa/analysis/tasks.py
index d8328eefd8a3d045357c9d98f1bd448409078b7e..86f8036e3c5478bd1adbe6775bd55eec1cfad80b 100644
--- a/lisa/analysis/tasks.py
+++ b/lisa/analysis/tasks.py
@@ -320,8 +320,12 @@ class TasksAnalysis(TraceAnalysisBase):
             df = df.collect()
 
         def finalize(df, key_col):
+            assert len(df.columns) == 2
             # Aggregate the values for each key and convert to python types
-            return dict(df.rows_by_key(key_col))
+            return {
+                key: [x[0] for x in values]
+                for key, values in df.rows_by_key(key_col).items()
+            }
 
         name_to_pid = finalize(df, 'name')
         pid_to_name = finalize(df, 'pid')
diff --git a/lisa/trace.py b/lisa/trace.py
index 5c27f66cb98d894bd444b5041f85bbfb5e5c0012..bf0110ec5e73ebc4040cc76b936daa1b5f254744 100644
--- a/lisa/trace.py
+++ b/lisa/trace.py
@@ -283,10 +283,14 @@ def _logical_plan_update_paths(plan, update_path):
                     else:
                         return paths
 
+                # The location is based on the version of polars, since the
+                # JSON format is unstable.
                 locs = [
                     ['paths'],
-                    # Since polars 1.7.0, paths are stored in a new location
-                    ['sources', 'sources', 'Paths']
+                    # 1.8.1
+                    ['sources', 'Paths'],
+                    # 1.7.0
+                    ['sources', 'sources', 'Paths'],
                 ]
                 for loc in locs:
                     try:
diff --git a/setup.py b/setup.py
index 07f03ee9c436eadea051ddab9ec485a9ab2d4800..4ee661f2cdfca1733eafbb603f6a02318f26dec6 100755
--- a/setup.py
+++ b/setup.py
@@ -137,8 +137,11 @@ if __name__ == "__main__":
             "panel",
             "colorcet",
             # Avoid:
-            # polars 1.7.0: https://github.com/pola-rs/polars/issues/18719
-            "polars >= 1.0.0, < 2.0.0, < 1.7.0",
+            # polars 1.7.0, 1.7.1: https://github.com/pola-rs/polars/issues/18719
+            # Require:
+            # polars >= 1.15.0: https://github.com/pola-rs/polars/issues/19994
+            # polars >= 1.16.0: https://github.com/pola-rs/polars/issues/20000
+            "polars >= 1.16.0, < 2.0.0",
             # Pandas >= 1.0.0 has support for new nullable dtypes
             # Pandas 1.2.0 has broken barplots:
             # https://github.com/pandas-dev/pandas/issues/38947
diff --git a/tests/test_trace.py b/tests/test_trace.py
index 78699612a67cc06f5d381148029026fefc1488ef..e6ed30ee0a407185fee6bbc96c279c2e1c26cfe1 100644
--- a/tests/test_trace.py
+++ b/tests/test_trace.py
@@ -154,8 +154,8 @@ class TraceTestCase(StorageTestCase):
             for x in (pid, name, task_id, task_id2, task_id3, task_id_tuple):
                 assert self.trace.ana.tasks.get_task_id(x) == task_id
 
-        with pytest.raises(ValueError):
-            for x in ('sh', 'sshd', 1639, 1642, 1702, 1717, 1718):
+        for x in ('sh', 'sshd'):
+            with pytest.raises(ValueError):
                 self.trace.ana.tasks.get_task_id(x)
 
     def test_get_task_name_pids(self):