diff --git a/implementations/Crafter.Debug-Session.cpp b/implementations/Crafter.Debug-Session.cpp
index 28d56e4..0176f47 100644
--- a/implementations/Crafter.Debug-Session.cpp
+++ b/implementations/Crafter.Debug-Session.cpp
@@ -16,7 +16,10 @@ import :Session;
 using namespace Crafter::Debug;
 using Crafter::Debug::Detail::Exchange;
 
-namespace {
+// Named, not anonymous: Session::State's members take these types, and a
+// type with internal linkage in the signature of one with module linkage is
+// an exposure clang warns about. Nothing here is exported.
+namespace Crafter::Debug::SessionImpl {
     using Clock = std::chrono::steady_clock;
 
     // Request parameters, decoded through Codec so a mistyped request is
@@ -245,6 +248,8 @@ namespace {
     };
 }
 
+using namespace Crafter::Debug::SessionImpl;
+
 namespace Crafter::Debug {
     struct Session::State {
         SessionOptions options;