diff --git a/src/poetry/core/constraints/generic/union_constraint.py b/src/poetry/core/constraints/generic/union_constraint.py
index 98b5ac411..75a5db800 100644
--- a/src/poetry/core/constraints/generic/union_constraint.py
+++ b/src/poetry/core/constraints/generic/union_constraint.py
@@ -141,7 +141,6 @@ def union(self, other: BaseConstraint) -> BaseConstraint:
             # just a special case of UnionConstraint
             other = UnionConstraint(other)
 
-        new_constraints: list[BaseConstraint] = []
         if isinstance(other, UnionConstraint):
             # (A or B) or (C or D) => A or B or C or D
             our_new_constraints: list[BaseConstraint] = []
@@ -179,6 +178,24 @@ def union(self, other: BaseConstraint) -> BaseConstraint:
             if any(c in other.constraints for c in self._constraints):
                 return self
 
+            # (A or B) or (not A and D) => A or B or D
+            simplified = False
+            our_simple_constraints = [
+                c for c in self._constraints if isinstance(c, Constraint)
+            ]
+            their_new_constraints = []
+            for their_constraint in other.constraints:
+                if any(
+                    c.union(their_constraint).is_any() for c in our_simple_constraints
+                ):
+                    simplified = True
+                else:
+                    their_new_constraints.append(their_constraint)
+            if simplified:
+                if not their_new_constraints:
+                    return AnyConstraint()
+                return self.union(UnionConstraint(*their_new_constraints))
+
             # (A or B) or (C and D) => nothing to do
             new_constraints = [*self._constraints, other]
 
diff --git a/tests/constraints/generic/test_constraint.py b/tests/constraints/generic/test_constraint.py
index c066c3cdc..fe4bc4d65 100644
--- a/tests/constraints/generic/test_constraint.py
+++ b/tests/constraints/generic/test_constraint.py
@@ -1129,20 +1129,12 @@ def test_intersect_extra(
         (
             UnionConstraint(Constraint("win32"), Constraint("linux")),
             MultiConstraint(Constraint("win32", "!="), Constraint("darwin", "!=")),
-            UnionConstraint(
-                Constraint("win32"),
-                Constraint("linux"),
-                MultiConstraint(Constraint("win32", "!="), Constraint("darwin", "!=")),
-            ),
+            Constraint("darwin", "!="),
         ),
         (
             UnionConstraint(Constraint("win32"), Constraint("linux")),
             MultiConstraint(Constraint("win32", "!="), Constraint("linux", "!=")),
-            UnionConstraint(
-                Constraint("win32"),
-                Constraint("linux"),
-                MultiConstraint(Constraint("win32", "!="), Constraint("linux", "!=")),
-            ),
+            AnyConstraint(),
         ),
         (
             MultiConstraint(Constraint("win32", "!="), Constraint("linux", "!=")),
@@ -1513,28 +1505,33 @@ def test_union(
         (
             UnionConstraint(ExtraConstraint("extra1"), ExtraConstraint("extra2")),
             ExtraMultiConstraint(
-                ExtraConstraint("extra1", "!="), ExtraConstraint("extra3", "!=")
+                ExtraConstraint("extra3", "!="), ExtraConstraint("extra4", "!=")
             ),
             UnionConstraint(
                 ExtraConstraint("extra1"),
                 ExtraConstraint("extra2"),
                 ExtraMultiConstraint(
-                    ExtraConstraint("extra1", "!="), ExtraConstraint("extra3", "!=")
+                    ExtraConstraint("extra3", "!="), ExtraConstraint("extra4", "!=")
                 ),
             ),
         ),
         (
             UnionConstraint(ExtraConstraint("extra1"), ExtraConstraint("extra2")),
             ExtraMultiConstraint(
-                ExtraConstraint("extra1", "!="), ExtraConstraint("extra2", "!=")
+                ExtraConstraint("extra1", "!="), ExtraConstraint("extra3", "!=")
             ),
             UnionConstraint(
                 ExtraConstraint("extra1"),
                 ExtraConstraint("extra2"),
-                ExtraMultiConstraint(
-                    ExtraConstraint("extra1", "!="), ExtraConstraint("extra2", "!=")
-                ),
+                ExtraConstraint("extra3", "!="),
+            ),
+        ),
+        (
+            UnionConstraint(ExtraConstraint("extra1"), ExtraConstraint("extra2")),
+            ExtraMultiConstraint(
+                ExtraConstraint("extra1", "!="), ExtraConstraint("extra2", "!=")
             ),
+            AnyConstraint(),
         ),
         (
             ExtraMultiConstraint(ExtraConstraint("extra1"), ExtraConstraint("extra2")),
diff --git a/tests/version/test_markers.py b/tests/version/test_markers.py
index acd877935..61c588225 100644
--- a/tests/version/test_markers.py
+++ b/tests/version/test_markers.py
@@ -717,12 +717,17 @@ def test_single_marker_union_with_inverse() -> None:
         (
             'extra != "a" and extra != "b"',
             'extra == "a" or extra == "b"',
-            'extra != "a" and extra != "b" or extra == "a" or extra == "b"',
+            "",
         ),
         (
             'extra != "a" and extra != "b"',
             'extra == "a" or extra == "c"',
-            'extra != "a" and extra != "b" or extra == "a" or extra == "c"',
+            'extra == "a" or extra == "c" or extra != "b"',
+        ),
+        (
+            'extra != "a" and extra != "b"',
+            'extra == "c" or extra == "d"',
+            'extra != "a" and extra != "b" or extra == "c" or extra == "d"',
         ),
         (
             'extra == "a" or extra == "b"',
@@ -1869,6 +1874,26 @@ def test_union_should_drop_markers_if_their_complement_is_present(
     assert parse_marker(expected) == m
 
 
+def test_inverse_atomic_markers() -> None:
+    m1 = parse_marker('sys_platform == "win32" or sys_platform == "linux"')
+    m2 = parse_marker('sys_platform != "win32" and sys_platform != "linux"')
+
+    assert m1.intersect(m2).is_empty()
+    assert m2.intersect(m1).is_empty()
+    assert m1.union(m2).is_any()
+    assert m2.union(m1).is_any()
+
+
+def test_partially_inverse_atomic_markers() -> None:
+    m1 = parse_marker('sys_platform == "win32" or sys_platform == "linux"')
+    m2 = parse_marker('sys_platform != "win32" and sys_platform != "darwin"')
+
+    assert str(m1.intersect(m2)) == 'sys_platform == "linux"'
+    assert str(m2.intersect(m1)) == 'sys_platform == "linux"'
+    assert str(m1.union(m2)) == 'sys_platform != "darwin"'
+    assert str(m2.union(m1)) == 'sys_platform != "darwin"'
+
+
 @pytest.mark.parametrize(
     "scheme, marker, expected",
     [