diff --git a/pyrit/common/apply_defaults.py b/pyrit/common/apply_defaults.py
index 7fdb7b8b22..c27b294444 100644
--- a/pyrit/common/apply_defaults.py
+++ b/pyrit/common/apply_defaults.py
@@ -106,6 +106,16 @@ def set_default_value(
             parameter_name=parameter_name,
             include_subclasses=include_subclasses,
         )
+        # A re-registration under the opposite flag replaces the previous one
+        # entirely; keeping both would leave the older value reachable (the
+        # lookup checks the include_subclasses=True scope first) and subclasses
+        # stuck inheriting it.
+        opposite_scope = DefaultValueScope(
+            class_type=class_type,
+            parameter_name=parameter_name,
+            include_subclasses=not include_subclasses,
+        )
+        self._default_values.pop(opposite_scope, None)
         self._default_values[scope] = value
         logger.debug(f"Set default value for {class_type.__name__}.{parameter_name} = {value}")
 
@@ -125,14 +135,18 @@ def get_default_value(
         Returns:
             Tuple of (found, value) where found indicates if a default was found.
         """
-        # First, try exact match
-        scope = DefaultValueScope(
-            class_type=class_type,
-            parameter_name=parameter_name,
-            include_subclasses=True,
-        )
-        if scope in self._default_values:
-            return True, self._default_values[scope]
+        # First, try exact match for both registration flags. A default
+        # registered with include_subclasses=False must still apply to the
+        # registered class itself - the flag only controls whether subclasses
+        # inherit the default.
+        for include_subclasses in (True, False):
+            scope = DefaultValueScope(
+                class_type=class_type,
+                parameter_name=parameter_name,
+                include_subclasses=include_subclasses,
+            )
+            if scope in self._default_values:
+                return True, self._default_values[scope]
 
         # Then, check parent classes if include_subclasses is True
         for existing_scope, value in self._default_values.items():
diff --git a/tests/unit/common/test_apply_defaults.py b/tests/unit/common/test_apply_defaults.py
index 77f472ee07..198a472cc4 100644
--- a/tests/unit/common/test_apply_defaults.py
+++ b/tests/unit/common/test_apply_defaults.py
@@ -98,6 +98,26 @@ def test_global_default_values_no_subclass_when_disabled():
     assert found is False
 
 
+def test_global_default_values_no_subclass_still_applies_to_base():
+    registry = GlobalDefaultValues()
+    registry.set_default_value(class_type=_Base, parameter_name="name", value="no-inherit", include_subclasses=False)
+    found, val = registry.get_default_value(class_type=_Base, parameter_name="name")
+    assert found is True
+    assert val == "no-inherit"
+    child = _Child()
+    assert child.name is None
+
+
+def test_global_default_values_mixed_flags_same_param():
+    registry = GlobalDefaultValues()
+    registry.set_default_value(class_type=_Base, parameter_name="name", value="base-only", include_subclasses=False)
+    registry.set_default_value(class_type=_Child, parameter_name="name", value="child-default")
+    found, val = registry.get_default_value(class_type=_Base, parameter_name="name")
+    assert found is True and val == "base-only"
+    found, val = registry.get_default_value(class_type=_Child, parameter_name="name")
+    assert found is True and val == "child-default"
+
+
 def test_global_default_values_reset():
     registry = GlobalDefaultValues()
     registry.set_default_value(class_type=_Base, parameter_name="name", value="x")
diff --git a/tests/unit/common/test_pyrit_default_value.py b/tests/unit/common/test_pyrit_default_value.py
index a6366ca615..40e2203b32 100644
--- a/tests/unit/common/test_pyrit_default_value.py
+++ b/tests/unit/common/test_pyrit_default_value.py
@@ -214,6 +214,47 @@ def __init__(
         assert child_obj.param2 == 50
         assert child_obj.param3 == 3.14
 
+    def test_reregistering_true_then_false_replaces_previous(self) -> None:
+        """True-then-False re-registration must replace the old scope, not shadow it."""
+
+        class TargetClass:
+            @apply_defaults
+            def __init__(self, *, param1: str | None = None) -> None:
+                self.param1 = param1
+
+        class ChildClass(TargetClass):
+            @apply_defaults
+            def __init__(self, *, param1: str | None = None) -> None:
+                super().__init__(param1=param1)
+
+        set_default_value(class_type=TargetClass, parameter_name="param1", value="broad", include_subclasses=True)
+        set_default_value(class_type=TargetClass, parameter_name="param1", value="exact", include_subclasses=False)
+
+        # The newer registration wins for the registered class itself...
+        assert TargetClass().param1 == "exact"
+        # ...and subclasses no longer inherit the removed True-scope default.
+        assert ChildClass().param1 is None
+
+    def test_reregistering_false_then_true_replaces_previous(self) -> None:
+        """False-then-True re-registration restores subclass inheritance."""
+
+        class TargetClass:
+            @apply_defaults
+            def __init__(self, *, param1: str | None = None) -> None:
+                self.param1 = param1
+
+        class ChildClass(TargetClass):
+            @apply_defaults
+            def __init__(self, *, param1: str | None = None) -> None:
+                super().__init__(param1=param1)
+
+        set_default_value(class_type=TargetClass, parameter_name="param1", value="exact", include_subclasses=False)
+        set_default_value(class_type=TargetClass, parameter_name="param1", value="broad", include_subclasses=True)
+
+        assert TargetClass().param1 == "broad"
+        # Subclass inheritance comes back with the restored True scope.
+        assert ChildClass().param1 == "broad"
+
     def test_parent_not_affected_by_child_defaults(self) -> None:
         """Test that setting defaults on child class doesn't affect parent instances."""