diff --git a/lib/AST/DistributedDecl.cpp b/lib/AST/DistributedDecl.cpp
index 3877139eefb39..8ab8b8ed5a4fb 100644
--- a/lib/AST/DistributedDecl.cpp
+++ b/lib/AST/DistributedDecl.cpp
@@ -488,8 +488,10 @@ bool AbstractFunctionDecl::isDistributedActorSystemRemoteCall(bool isVoidReturn)
   }
 
   // === Must be declared in a 'DistributedActorSystem' conforming type
-  ProtocolDecl *systemProto =
-      C.getDistributedActorSystemDecl();
+  ProtocolDecl *systemProto = C.getDistributedActorSystemDecl();
+  if (!systemProto) {
+    return false;
+  }
 
   auto systemNominal = DC->getSelfNominalTypeDecl();
   auto distSystemConformance = lookupConformance(
@@ -794,6 +796,9 @@ AbstractFunctionDecl::isDistributedTargetInvocationEncoderRecordArgument() const
   // === Must be declared in a 'DistributedTargetInvocationEncoder' conforming type
   ProtocolDecl *encoderProto =
       C.getProtocol(KnownProtocolKind::DistributedTargetInvocationEncoder);
+  if (!encoderProto) {
+    return false;
+  }
 
   auto encoderNominal = getDeclContext()->getSelfNominalTypeDecl();
   auto protocolConformance = lookupConformance(
@@ -925,6 +930,9 @@ AbstractFunctionDecl::isDistributedTargetInvocationEncoderRecordReturnType() con
   // === Must be declared in a 'DistributedTargetInvocationEncoder' conforming type
   ProtocolDecl *encoderProto =
       C.getProtocol(KnownProtocolKind::DistributedTargetInvocationEncoder);
+  if (!encoderProto) {
+    return false;
+  }
 
   auto encoderNominal = getDeclContext()->getSelfNominalTypeDecl();
   auto protocolConformance = lookupConformance(
@@ -1051,6 +1059,9 @@ AbstractFunctionDecl::isDistributedTargetInvocationEncoderRecordErrorType() cons
     // === Must be declared in a 'DistributedTargetInvocationEncoder' conforming type
     ProtocolDecl *encoderProto =
         C.getProtocol(KnownProtocolKind::DistributedTargetInvocationEncoder);
+    if (!encoderProto) {
+      return false;
+    }
 
     auto encoderNominal = getDeclContext()->getSelfNominalTypeDecl();
     auto protocolConformance = lookupConformance(
@@ -1158,7 +1169,9 @@ AbstractFunctionDecl::isDistributedTargetInvocationDecoderDecodeNextArgument() c
     // === Must be declared in a 'DistributedTargetInvocationEncoder' conforming type
     ProtocolDecl *decoderProto =
         C.getProtocol(KnownProtocolKind::DistributedTargetInvocationDecoder);
-
+    if (!decoderProto) {
+      return false;
+    }
     auto decoderNominal = getDeclContext()->getSelfNominalTypeDecl();
     auto protocolConformance = lookupConformance(
         decoderNominal->getDeclaredInterfaceType(), decoderProto);
@@ -1251,6 +1264,9 @@ AbstractFunctionDecl::isDistributedTargetInvocationResultHandlerOnReturn() const
     // === Must be declared in a 'DistributedTargetInvocationEncoder' conforming type
     ProtocolDecl *decoderProto =
         C.getProtocol(KnownProtocolKind::DistributedTargetInvocationResultHandler);
+    if (!decoderProto) {
+      return false;
+    }
 
     auto decoderNominal = getDeclContext()->getSelfNominalTypeDecl();
     auto protocolConformance = lookupConformance(
diff --git a/test/Distributed/distributed_actor_adhoc_names_in_non_da_types.swift b/test/Distributed/distributed_actor_adhoc_names_in_non_da_types.swift
new file mode 100644
index 0000000000000..8516b1e3742df
--- /dev/null
+++ b/test/Distributed/distributed_actor_adhoc_names_in_non_da_types.swift
@@ -0,0 +1,82 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend-emit-module -emit-module-path %t/FakeDistributedActorSystems.swiftmodule -module-name FakeDistributedActorSystems -target %target-swift-5.7-abi-triple %S/Inputs/FakeDistributedActorSystems.swift
+// RUN: %target-swift-frontend -typecheck -verify -target %target-swift-5.7-abi-triple -I %t 2>&1 %s
+
+// UNSUPPORTED: back_deploy_concurrency
+// REQUIRES: concurrency
+// REQUIRES: distributed
+
+import Distributed
+import FakeDistributedActorSystems
+
+distributed actor Philosopher {
+  typealias ActorSystem = FakeActorSystem
+
+  let philosophy: String
+
+  init(system: FakeActorSystem) {
+    philosophy = "Epistemology"
+  }
+
+  distributed func hi1() -> String { "Hi!" }
+//  distributed func hi2() -> String { "Hi!" }
+//  distributed func hi3() -> String { "Hi!" }
+//  distributed func hi4() -> String { "Hi!" }
+//  distributed func hi5() -> String { "Hi!" }
+//  distributed func hi6() -> String { "Hi!" }
+//  distributed func hi7() -> String { "Hi!" }
+//  distributed func hi8() -> String { "Hi!" }
+//  distributed func hi9() -> String { "Hi!" }
+
+  func test(other: Philosopher) async throws {
+    // self --------------------------------------------------------------------
+    async let alet = self.hi1() // none
+    _ = await alet // Ok - `self.hi()` isn't throwing
+
+//    Task {
+//      _ = self.hi1() // none
+//    }
+//
+//    Task.detached {
+//      _ = await self.hi2() // async
+//    }
+  }
+
+//    // other -------------------------------------------------------------------
+//
+//    async let otherLet = other.hi3() // hi = async throws because of `other`
+//    _ = try await otherLet
+//
+//    Task {
+//      _ = try await other.hi4() // hi = async throws
+//    }
+//
+//    Task.detached {
+//      _ = try await other.hi5() // hi = async throws
+//    }
+//
+//    // known to be local -------------------------------------------------------
+//
+//    // FIXME(distributed): relies on the "secretly known to be local" hack in typechecking
+//    let _: String? = await other.whenLocal { __secretlyKnownToBeLocal in
+//      // we're able to get state of what would otherwise be distributed-isolated:
+//      __secretlyKnownToBeLocal.philosophy
+//    }
+//  }
+//
+//  static func test(iso: isolated Philosopher) async throws {
+//    _ = iso.h6() // we're "in the actor" already, since isolated
+//
+//    // isolated parameter ------------------------------------------------------
+//    async let otherLet = iso.hi7() // async
+//    _ = await otherLet
+//
+//    Task {
+//      _ = await iso.hi8() // none
+//    }
+//
+//    Task.detached {
+//      _ = await iso.hi9() // async
+//    }
+//  }
+}