diff --git a/src/tools/moc/moc.cpp b/src/tools/moc/moc.cpp
index 36d84a61d8e..4d3ccb86802 100644
--- a/src/tools/moc/moc.cpp
+++ b/src/tools/moc/moc.cpp
@@ -559,6 +559,9 @@ void Moc::parse()
                     if (test(EQ)) {
                         // namespace Foo = Bar::Baz;
                         until(SEMIC);
+                    } else if (test(LPAREN)) {
+                        // Ignore invalid code such as: 'namespace __identifier("x")' (QTBUG-56634)
+                        until(RPAREN);
                     } else if (!test(SEMIC)) {
                         NamespaceDef def;
                         def.classname = nsName;
diff --git a/tests/auto/tools/moc/namespace.h b/tests/auto/tools/moc/namespace.h
index 6e048315897..43d00e82f3e 100644
--- a/tests/auto/tools/moc/namespace.h
+++ b/tests/auto/tools/moc/namespace.h
@@ -74,4 +74,8 @@ namespace FooNamespace {
     }
 }
 
+#ifdef Q_MOC_RUN
+namespace __identifier("<AtlImplementationDetails>") {} // QTBUG-56634
+#endif
+
 #endif // NAMESPACE_H