From 385d754fcd312c11a8308be7353e7b969328495b Mon Sep 17 00:00:00 2001
From: timmens <mensingertim@gmail.com>
Date: Fri, 30 Oct 2026 14:43:57 +0100
Subject: [PATCH] Preserve restrictive infinite bounds during normalization

---
 src/optimagic/parameters/bounds.py        |  8 +++---
 tests/optimagic/parameters/test_bounds.py | 34 +++++++++++++++++++++++
 2 files changed, 38 insertions(+), 4 deletions(-)

diff --git a/src/optimagic/parameters/bounds.py b/src/optimagic/parameters/bounds.py
index 8e26022db..a4075cb75 100644
--- a/src/optimagic/parameters/bounds.py
+++ b/src/optimagic/parameters/bounds.py
@@ -156,9 +156,9 @@ def get_internal_bounds(
         msg = "Invalid bounds. Some lower bounds are larger than upper bounds."
         raise InvalidBoundsError(msg)
 
-    if np.isinf(lower_flat).all():
+    if np.isneginf(lower_flat).all():
         lower_flat = None
-    if np.isinf(upper_flat).all():
+    if np.isposinf(upper_flat).all():
         upper_flat = None
 
     return lower_flat, upper_flat
@@ -245,14 +245,14 @@ def _get_fast_path_bounds(
         lower_bounds = None
     else:
         lower_bounds = bounds.lower.astype(float)
-        if np.isinf(lower_bounds).all():
+        if np.isneginf(lower_bounds).all():
             lower_bounds = None
 
     if bounds.upper is None:
         upper_bounds = None
     else:
         upper_bounds = bounds.upper.astype(float)
-        if np.isinf(upper_bounds).all():
+        if np.isposinf(upper_bounds).all():
             upper_bounds = None
 
     if (
diff --git a/tests/optimagic/parameters/test_bounds.py b/tests/optimagic/parameters/test_bounds.py
index a6c3f487a..ac71de549 100644
--- a/tests/optimagic/parameters/test_bounds.py
+++ b/tests/optimagic/parameters/test_bounds.py
@@ -138,6 +138,40 @@ def test_get_bounds_numpy_error(array_params):
         )
 
 
+@pytest.mark.parametrize("container", [np.array, list])
+@pytest.mark.parametrize(
+    "lower, upper, expected_lower, expected_upper",
+    [
+        ([-np.inf, -np.inf], [np.inf, np.inf], None, None),
+        ([np.inf, np.inf], None, [np.inf, np.inf], None),
+        (None, [-np.inf, -np.inf], None, [-np.inf, -np.inf]),
+        ([-np.inf, np.inf], None, [-np.inf, np.inf], None),
+        (None, [-np.inf, np.inf], None, [-np.inf, np.inf]),
+    ],
+)
+def test_get_bounds_infinite_sides(
+    container, lower, upper, expected_lower, expected_upper
+):
+    bounds = Bounds(
+        lower=None if lower is None else container(lower),
+        upper=None if upper is None else container(upper),
+    )
+
+    got_lower, got_upper = get_internal_bounds(np.ones(2), bounds=bounds)
+
+    assert_array_equal(got_lower, expected_lower)
+    assert_array_equal(got_upper, expected_upper)
+
+
+@pytest.mark.parametrize("container", [np.array, list])
+@pytest.mark.parametrize("lower, upper", [(np.inf, 5), (0, -np.inf), (np.inf, -np.inf)])
+def test_get_bounds_infinite_sides_invalid(container, lower, upper):
+    bounds = Bounds(lower=container([lower, lower]), upper=container([upper, upper]))
+
+    with pytest.raises(InvalidBoundsError):
+        get_internal_bounds(np.ones(2), bounds=bounds)
+
+
 def test_get_fast_path_bounds_both_none():
     got_lower, got_upper = _get_fast_path_bounds(Bounds(lower=None, upper=None))
     assert got_lower is None