diff --git a/packages/@jsii/python-runtime/src/jsii/_reference_map.py b/packages/@jsii/python-runtime/src/jsii/_reference_map.py
index 8d5a78ec89..e10db5ec09 100644
--- a/packages/@jsii/python-runtime/src/jsii/_reference_map.py
+++ b/packages/@jsii/python-runtime/src/jsii/_reference_map.py
@@ -142,7 +142,7 @@ def resolve(self, kernel, ref):
         except KeyError:
             pass
 
-        # If we got to this point, then we didn't have a referene for this, in that case
+        # If we got to this point, then we didn't have a reference for this, in that case
         # we want to create a new instance, but we need to create it in such a way that
         # we don't try to recreate the type inside of the JSII interface.
         class_fqn = ref.ref.rsplit("@", 1)[0]
@@ -242,7 +242,16 @@ def resolve_id(self, id: str) -> Any:
         return self._refs[id]
 
     def build_interface_proxies_for_ref(self, ref: ObjRef) -> List[Any]:
-        ifaces = [_obtain_interface(fqn) for fqn in ref.interfaces or []]
+        fqns = ref.interfaces or []
+        for fqn in fqns:
+            if fqn not in _data_types and fqn not in _interfaces:
+                _try_import_type_module(fqn)
+
+        # A struct FQN can show up in the ref.interfaces when a value is typed as
+        # a union of a behavioral interface and a struct (e.g. foo: IResolvable | SomeProperty
+        # that appears on many L1 constructs). Skip structs instead of treating them
+        # as an unknown behavioral interface.
+        ifaces = [_obtain_interface(fqn) for fqn in fqns if fqn not in _data_types]
         classes = [iface.__jsii_proxy_class__() for iface in ifaces]
 
         # If there's no classes, use an Opaque reference to make sure the
diff --git a/packages/@jsii/python-runtime/tests/test_compliance.py b/packages/@jsii/python-runtime/tests/test_compliance.py
index d4f3682626..e92955b15d 100644
--- a/packages/@jsii/python-runtime/tests/test_compliance.py
+++ b/packages/@jsii/python-runtime/tests/test_compliance.py
@@ -87,10 +87,13 @@
 )
 from jsii_calc.submodule.isolated import Kwargs
 from jsii_calc.submodule.child import SomeEnum
+from jsii_calc.union import Resolvable
 from scope.jsii_calc_lib import IFriendly, EnumFromScopedModule, Number
 from scope.jsii_calc_lib.custom_submodule_name import IReflectable, ReflectableEntry
 from scope.jsii_calc_lib.deprecation_removal import InterfaceFactory
 
+from jsii._reference_map import InterfaceDynamicProxy
+
 # Note: The names of these test functions have been chosen to map as closely to the
 #       Java Compliance tests as possible.
 # Note: While we could write more expressive and better tests using the functionality
@@ -1447,6 +1450,95 @@ def get(self, _ref, _name):
     assert isinstance(result, _reference_map._data_types[struct_fqn])
 
 
+def test_known_class_ref_with_struct_in_interfaces_resolves():
+    """
+    Verifies resolving an object reference whose primary type is a known
+    class, but whose ``interfaces`` list contains an unrelated struct
+    FQN, does not raise an Unknown interface exception. And that the known
+    class instance ends up as the proxy's primary delegate.
+
+    This shape occurs for properties typed as a union of a behavioral
+    interface and a struct, such as ``ConsumesUnion.union_property``
+    (``IResolvable | UnionResolvableStruct`` below), which mirrors AWS CDK
+    shapes like ``CfnLaunchTemplate.launchTemplateData: IResolvable |
+    LaunchTemplateDataProperty``.
+
+    The shape is produced by the kernel as follows:
+
+    - The kernel tries each union member's serializer in a fixed
+      priority order and uses the first one that doesn't throw an exception.
+
+        - SerializationClass.Void,
+        - SerializationClass.Date,
+        - SerializationClass.Scalar,
+        - SerializationClass.Json,
+        - SerializationClass.Enum,
+        - SerializationClass.Array,
+        - SerializationClass.Map,
+        - SerializationClass.Struct,
+        - SerializationClass.ReferenceType,
+        - SerializationClass.Any,
+
+      ``Struct`` serialization checks that the value is a non-null,
+      non-array, non-``Date`` object. Any object value matching that
+      criteria is serialized as a struct even if the real type is actually
+      the ``interface`` half of the union. From the example above, setting
+      the ``launchTemplateData`` property to ``Fn.condition_if`` sets the true
+      class as ``Intrinsic`` which implements the ``IResolvable`` interface.
+
+    - When Struct.serialize calls registerObject(value, "Object", ["...SomeDataProperty"]),
+      and the value was already registered under it's true class (``Intrinsic``), the identity
+      cache merges interfaces into the existing entry instead of creating a new one. That is
+      how a reference whose primary type is a known class ends up with a unrelated struct
+      FQN riding along in ``ref.interfaces``.
+
+      class_fqn='aws-cdk-lib.Intrinsic' ref.interfaces=['aws-cdk-lib.ICfnRuleConditionExpression']
+      ...
+      class_fqn='aws-cdk-lib.Intrinsic' ref.interfaces=['aws-cdk-lib.ICfnRuleConditionExpression', 'aws-cdk-lib.aws_ec2.CfnLaunchTemplate.LaunchTemplateDataProperty']
+
+    ``resolve()``'s "known class" branch (``class_fqn in _types``) used to
+    invoke ``_obtain_interface`` for every item in ``ref.interfaces``. If
+    ``ref.interfaces`` contained an entry for a struct registered in
+    ``_data_types``, then ``_obtain_interface`` would be unable to find
+    the interace and raise a ``ValueError``. To avoid the issue, the logic
+    now filters out any FQN in the ``_data_types`` map before invoking
+    ``_obtain_interface``.
+
+    This test simulates that exact shape with a synthetic ``ObjRef`` (a known
+    class FQN as the primary type, an unrelated struct FQN in ``interfaces``)
+    and checks not just that resolution succeeds, but that it produces the
+    *correct* result: the known ``Resolvable`` instance as the proxy's
+    primary delegate, and the struct FQN represented by an opaque fallback
+    delegate rather than being dropped, misidentified, or raising.
+    """
+    from jsii import _reference_map
+    from jsii._kernel.types import ObjRef
+
+    # FQNs of ConsumesUnion.union_property's `IResolvable | UnionResolvableStruct`
+    # union members (see packages/jsii-calc/lib/union.ts).
+    class_fqn = "jsii-calc.union.Resolvable"
+    struct_fqn = "jsii-calc.union.UnionResolvableStruct"
+
+    # Simulate the kernel returning a reference to a known Resolvable instance
+    # that also lists the struct's FQN in its interfaces -- the shape produced
+    # for union-typed values.
+    ref = ObjRef(ref=f"{class_fqn}@90127", interfaces=[struct_fqn])
+
+    # This must NOT raise: the struct FQN is recognized and skipped rather
+    # than treated as an (unknown) behavioral interface.
+    result = _reference_map.resolve_reference(jsii.kernel, ref)
+    assert result is not None
+    assert isinstance(result, InterfaceDynamicProxy)
+
+    # The known Resolvable instance should be the proxy's
+    # primary delegate, with the struct FQN represented as
+    # an opaque fallback rather than an (unknown) behavioral
+    # interface.
+    assert isinstance(result._delegates[0], Resolvable)
+    assert isinstance(result._delegates[1], _reference_map.Opaque)
+    assert result._delegates[1].__jsii_ref__ == ref
+
+
 def test_stripped_deprecated_member_can_be_received():
     assert InterfaceFactory.create() is not None
 
diff --git a/packages/jsii-calc/lib/union.ts b/packages/jsii-calc/lib/union.ts
index ef4bf22b8f..692ffb8cf1 100644
--- a/packages/jsii-calc/lib/union.ts
+++ b/packages/jsii-calc/lib/union.ts
@@ -12,10 +12,16 @@ export class Resolvable implements IResolvable {
   }
 }
 
+export interface UnionResolvableStruct {
+  readonly value: string;
+}
+
 export class ConsumesUnion {
   public static unionType(param: IResolvable | Resolvable | IFriendly) {
     void param;
   }
 
+  public unionProperty?: IResolvable | UnionResolvableStruct;
+
   private constructor() {}
 }