diff --git a/docs/scripts/api_generator.py b/docs/scripts/api_generator.py
index 038ed9dd..62a9048c 100644
--- a/docs/scripts/api_generator.py
+++ b/docs/scripts/api_generator.py
@@ -2,6 +2,7 @@
 
 # https://mkdocstrings.github.io/recipes/
 """
+
 from __future__ import annotations
 
 import logging
diff --git a/docs/scripts/debug_which_page_is_being_rendered.py b/docs/scripts/debug_which_page_is_being_rendered.py
index 5f8b642f..efbe40ed 100644
--- a/docs/scripts/debug_which_page_is_being_rendered.py
+++ b/docs/scripts/debug_which_page_is_being_rendered.py
@@ -3,6 +3,7 @@
 
 This makes it easier to identify which file is being rendered when an error happens.
 """
+
 from __future__ import annotations
 
 import logging
@@ -16,6 +17,7 @@
 
 log = logging.getLogger("mkdocs")
 
+
 def on_pre_page(
     page: mkdocs.structure.pages.Page,
     config: Any,
diff --git a/src/ConfigSpace/forbidden.py b/src/ConfigSpace/forbidden.py
index 4b6ba0d4..5eb535db 100644
--- a/src/ConfigSpace/forbidden.py
+++ b/src/ConfigSpace/forbidden.py
@@ -614,13 +614,18 @@ def is_forbidden_vector(self, vector: Array[f64]) -> bool:
         # Relation is always evaluated against actual value and not vector rep
         left: f64 = vector[self.vector_ids[0]]  # type: ignore
         right: f64 = vector[self.vector_ids[1]]  # type: ignore
+        if np.isnan(left) or np.isnan(right):
+            return False
         return self.left.to_value(left) < self.right.to_value(right)  # type: ignore
 
     @override
     def is_forbidden_vector_array(self, arr: Array[f64]) -> Mask:
         left = arr[self.vector_ids[0]]
         right = arr[self.vector_ids[1]]
-        return self.left.to_value(left) < self.right.to_value(right)
+        valid = ~(np.isnan(left) | np.isnan(right))
+        out = np.zeros_like(valid)
+        out[valid] = self.left.to_value(left[valid]) < self.right.to_value(right[valid])
+        return out
 
 
 class ForbiddenEqualsRelation(ForbiddenRelation):
@@ -680,13 +685,19 @@ def is_forbidden_vector(self, vector: Array[f64]) -> bool:
         # Relation is always evaluated against actual value and not vector rep
         left = vector[self.vector_ids[0]]
         right = vector[self.vector_ids[1]]
+        if np.isnan(left) or np.isnan(right):
+            return False
         return self.left.to_value(left) == self.right.to_value(right)  # type: ignore
 
     @override
     def is_forbidden_vector_array(self, arr: Array[f64]) -> Mask:
         left = arr[self.vector_ids[0]]
         right = arr[self.vector_ids[1]]
-        return self.left.to_value(left) == self.right.to_value(right)  # type: ignore
+        valid = ~(np.isnan(left) | np.isnan(right))
+        tmp = self.left.to_value(left[valid]) == self.right.to_value(right[valid])
+        out = np.zeros_like(valid)
+        out[valid] = tmp
+        return out  # type: ignore
 
 
 class ForbiddenGreaterThanRelation(ForbiddenRelation):
@@ -745,13 +756,18 @@ def is_forbidden_vector(self, vector: Array[f64]) -> bool:
         # Relation is always evaluated against actual value and not vector rep
         left: f64 = vector[self.vector_ids[0]]  # type: ignore
         right: f64 = vector[self.vector_ids[1]]  # type: ignore
+        if np.isnan(left) or np.isnan(right):
+            return False
         return self.left.to_value(left) > self.right.to_value(right)  # type: ignore
 
     @override
     def is_forbidden_vector_array(self, arr: Array[f64]) -> Mask:
         left = arr[self.vector_ids[0]]
         right = arr[self.vector_ids[1]]
-        return self.left.to_value(left) > self.right.to_value(right)
+        valid = ~(np.isnan(left) | np.isnan(right))
+        out = np.zeros_like(valid)
+        out[valid] = self.left.to_value(left[valid]) > self.right.to_value(right[valid])
+        return out
 
 
 ForbiddenLike = Union[
diff --git a/test/test_forbidden.py b/test/test_forbidden.py
index f297a6a8..7f47b881 100644
--- a/test/test_forbidden.py
+++ b/test/test_forbidden.py
@@ -291,3 +291,23 @@ def test_relation():
     assert forb.is_forbidden_value(
         {"water_temperature": "hot", "water_temperature2": "cold"},
     )
+
+
+def test_relation_conditioned():
+    from ConfigSpace import EqualsCondition, ConfigurationSpace
+
+    a = OrdinalHyperparameter("a", [2, 5, 10])
+    enable_a = CategoricalHyperparameter("enable_a", [False, True], weights=[99999, 1])
+    cond_a = EqualsCondition(a, enable_a, True)
+
+    b = OrdinalHyperparameter("b", [5, 10, 15])
+    for forbid in (
+        ForbiddenEqualsRelation,
+        ForbiddenGreaterThanRelation,
+        ForbiddenLessThanRelation,
+    ):
+        forbid_a_b = forbid(a, b)
+
+        cs = ConfigurationSpace()
+        cs.add([a, enable_a, cond_a, b, forbid_a_b])
+        cs.sample_configuration(100)