diff --git a/pkgs/development/python-modules/vegafusion/default.nix b/pkgs/development/python-modules/vegafusion/default.nix
index c53d97e00fdc..1feb046ad299 100644
--- a/pkgs/development/python-modules/vegafusion/default.nix
+++ b/pkgs/development/python-modules/vegafusion/default.nix
@@ -37,6 +37,10 @@ buildPythonPackage rec {
     hash = "sha256-yiECw9WGd+03KFOWa+bwR10gQFqzx4Riy6uw2zwdc3s=";
   };
 
+  patches = [
+    ./fix-test_transformer.patch
+  ];
+
   cargoDeps = rustPlatform.fetchCargoVendor {
     inherit src;
     name = "${pname}-${version}";
diff --git a/pkgs/development/python-modules/vegafusion/fix-test_transformer.patch b/pkgs/development/python-modules/vegafusion/fix-test_transformer.patch
new file mode 100644
index 000000000000..71c14c2bf78d
--- /dev/null
+++ b/pkgs/development/python-modules/vegafusion/fix-test_transformer.patch
@@ -0,0 +1,47 @@
+From 5ba473229913031b2b3053371db7887d23b45ff8 Mon Sep 17 00:00:00 2001
+From: Mario <191101255+wariuccio@users.noreply.github.com>
+Date: Tue, 14 Jul 2026 20:10:05 +0100
+Subject: [PATCH] Relax data type checks in `test_transformer.py`
+
+https://github.com/vega/vegafusion/issues/591
+---
+ vegafusion-python/tests/test_transformer.py | 14 ++++++++++----
+ 1 file changed, 10 insertions(+), 4 deletions(-)
+
+diff --git a/vegafusion-python/tests/test_transformer.py b/vegafusion-python/tests/test_transformer.py
+index 8852bb068..fe7f87e1e 100644
+--- a/vegafusion-python/tests/test_transformer.py
++++ b/vegafusion-python/tests/test_transformer.py
+@@ -17,7 +17,7 @@ def test_to_arrow_expands_categoricals():
+ 
+     # Check that pyarrow type is String (not Dictionary)
+     b_type = pa_table.column("b").type
+-    assert b_type == pa.string()
++    assert b_type == pa.string() or b_type == pa.large_string()
+ 
+ 
+ def test_to_table_converts_decimals():
+@@ -45,7 +45,7 @@ def test_to_table_with_mixed_string_int_column():
+ 
+     # Check that pyarrow type is float64 (not Decimal128)
+     b_type = pa_table.column("b").type
+-    assert b_type == pa.string()
++    assert b_type == pa.string() or b_type == pa.large_string()
+ 
+ 
+ def test_to_table_with_all_conversions():
+@@ -68,6 +68,12 @@ def test_to_table_with_all_conversions():
+     pa_table = to_arrow_table(df)
+ 
+     # Check pyarrow types
+-    assert pa_table.column("b").type == pa.string()
++    assert (
++        pa_table.column("b").type == pa.string()
++        or pa_table.column("b").type == pa.large_string()
++    )
+     assert pa_table.column("c").type == pa.float64()
+-    assert pa_table.column("d").type == pa.string()
++    assert (
++        pa_table.column("d").type == pa.string()
++        or pa_table.column("d").type == pa.large_string()
++    )