diff --git a/src/pyrecest/backend_tools.py b/src/pyrecest/backend_tools.py
index edb09ba5b..0703b8ad0 100644
--- a/src/pyrecest/backend_tools.py
+++ b/src/pyrecest/backend_tools.py
@@ -34,7 +34,7 @@ def _normalize_expected_backend_names(
         not isinstance(name, str) or not name or name.strip() != name for name in names
     ):
         raise ValueError(message)
-    return names
+    return tuple(dict.fromkeys(names))
 
 
 def assert_backend(expected: str | tuple[str, ...]) -> None:
diff --git a/tests/test_backend_tools.py b/tests/test_backend_tools.py
index b02416994..85dfa1f99 100644
--- a/tests/test_backend_tools.py
+++ b/tests/test_backend_tools.py
@@ -19,6 +19,16 @@ def test_assert_backend_rejects_unexpected_backend():
         pyrecest.assert_backend(unexpected)
 
 
+def test_assert_backend_deduplicates_expected_names_in_error_message():
+    active = pyrecest.get_backend_name()
+    unexpected = "jax" if active != "jax" else "numpy"
+
+    with pytest.raises(RuntimeError) as excinfo:
+        pyrecest.assert_backend((unexpected, unexpected))
+
+    assert str(excinfo.value).count(unexpected) == 1
+
+
 @pytest.mark.parametrize(
     "expected", [(), ("",), " ", (" numpy",), ("numpy ",), ("numpy", 1), 1]
 )