diff --git a/CMakeLists.txt b/CMakeLists.txt
index e66d252..b3007c0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -116,6 +116,10 @@ if(XYZ_PROTOCOL_IS_NOT_SUBPROJECT)
       CLASS_NAME C INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/interface_C.h
       HEADER interface_C.h
       OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/generated/protocol_C.h ${OPT_MANUAL_VTABLE})
+    xyz_generate_protocol(
+      CLASS_NAME Demo INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/demo.h
+      HEADER demo.h
+      OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/generated/protocol_demo.h ${OPT_MANUAL_VTABLE})
 
     add_custom_target(
       generate_protocols
@@ -123,7 +127,8 @@ if(XYZ_PROTOCOL_IS_NOT_SUBPROJECT)
               ${CMAKE_CURRENT_BINARY_DIR}/generated/protocol_A_virtual.h
               ${CMAKE_CURRENT_BINARY_DIR}/generated/protocol_A_manual.h
               ${CMAKE_CURRENT_BINARY_DIR}/generated/protocol_B.h
-              ${CMAKE_CURRENT_BINARY_DIR}/generated/protocol_C.h)
+              ${CMAKE_CURRENT_BINARY_DIR}/generated/protocol_C.h
+              ${CMAKE_CURRENT_BINARY_DIR}/generated/protocol_demo.h)
 
     xyz_add_test(
       NAME
diff --git a/demo.h b/demo.h
new file mode 100644
index 0000000..f970e5f
--- /dev/null
+++ b/demo.h
@@ -0,0 +1,12 @@
+#ifndef XYZ_PROTOCOL_DEMO_H
+#define XYZ_PROTOCOL_DEMO_H
+
+namespace xyz {
+
+struct Demo {
+  int call(int) const;
+};
+
+}  // namespace xyz
+
+#endif  // XYZ_PROTOCOL_DEMO_H
diff --git a/protocol_test.cc b/protocol_test.cc
index eae1934..b80437d 100644
--- a/protocol_test.cc
+++ b/protocol_test.cc
@@ -30,6 +30,7 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 #include "generated/protocol_A.h"
 #include "generated/protocol_B.h"
 #include "generated/protocol_C.h"
+#include "generated/protocol_demo.h"
 #include "tracking_allocator.h"
 
 namespace {
@@ -626,4 +627,13 @@ TEST(ProtocolViewTest, ViewMoveIsStandard) {
   EXPECT_EQ(view2.name(), "move_test");
 }
 
+struct Demoic {
+  int call(int x) const { return x * 2; }
+};
+
+TEST(ProtocolDemoTest, DemoFunction) {
+  xyz::protocol<xyz::Demo> demo(std::in_place_type<Demoic>);
+  EXPECT_EQ(demo.call(5), 10);
+}
+
 }  // namespace