diff --git a/cmake/xo_macros/xo_cxx.cmake b/cmake/xo_macros/xo_cxx.cmake
index ba43b34e..182f1599 100644
--- a/cmake/xo_macros/xo_cxx.cmake
+++ b/cmake/xo_macros/xo_cxx.cmake
@@ -1646,14 +1646,17 @@ macro(xo_add_genfacet)
         REQUIRED)
     message(STATUS "GENFACET_EXECUTABLE=${GENFACET_EXECUTABLE}")
 
+    set(generatedFiles
+        ${GF_OUTPUT_HPP_DIR}/${FACET}.hpp
+        ${GF_OUTPUT_HPP_DIR}/${GF_OUTPUT_IMPL_SUBDIR}/A${FACET}.hpp
+        ${GF_OUTPUT_HPP_DIR}/${GF_OUTPUT_IMPL_SUBDIR}/I${FACET}_Any.hpp
+        ${GF_OUTPUT_HPP_DIR}/${GF_OUTPUT_IMPL_SUBDIR}/I${FACET}_Xfer.hpp
+        ${GF_OUTPUT_HPP_DIR}/${GF_OUTPUT_IMPL_SUBDIR}/R${FACET}.hpp
+        ${GF_OUTPUT_CPP_DIR}/I${FACET}_Any.cpp)
+
     # Build the genfacet command
     add_custom_command(
-        OUTPUT ${GF_OUTPUT_HPP_DIR}/${FACET}.hpp
-            ${GF_OUTPUT_HPP_DIR}/${GF_OUTPUT_IMPL_SUBDIR}/A${FACET}.hpp
-            ${GF_OUTPUT_HPP_DIR}/${GF_OUTPUT_IMPL_SUBDIR}/I${FACET}_Any.hpp
-            ${GF_OUTPUT_HPP_DIR}/${GF_OUTPUT_IMPL_SUBDIR}/I${FACET}_Xfer.hpp
-            ${GF_OUTPUT_HPP_DIR}/${GF_OUTPUT_IMPL_SUBDIR}/R${FACET}.hpp
-            ${GF_OUTPUT_CPP_DIR}/I${FACET}_Any.cpp
+        OUTPUT $generatedFiles
         COMMAND ${GENFACET_EXECUTABLE}
             --input ${GF_INPUT}
             --output-hpp ${GF_OUTPUT_HPP_DIR}
@@ -1666,7 +1669,50 @@ macro(xo_add_genfacet)
     )
 
     # Create a target for this generation
-    add_custom_target(${GF_TARGET}
-        DEPENDS ${GF_GENERATED_FILES}
-    )
+    add_custom_target(${GF_TARGET} DEPENDS ${generatedFiles})
+endmacro()
+
+macro(xo_add_genfacetimpl)
+    # Parse arguments
+    set(options "")
+    set(oneValueArgs
+        TARGET              # Name for this generation target
+        FACET               # facet name
+        REPR                # representation name
+        INPUT               # Input .json5 file
+        OUTPUT_HPP_DIR      # Directory for .hpp files
+        OUTPUT_IMPL_SUBDIR  # Subdirectory name for impl headers
+        OUTPUT_CPP_DIR      # Directory for .cpp files
+    )
+    set(multiValueArgs "")
+
+    cmake_parse_arguments(GF "${options}" "${oneValueArgs}" "${multiValueArgs}" ${ARGN})
+
+    find_program(GENFACET_EXECUTABLE NAMES genfacet
+        HINTS ${CMAKE_SOURCE_DIR}/xo-facet/codegen
+        DOC "path to xo genfacet code generator"
+        REQUIRED)
+    message(STATUS "GENFACET_EXECUTABLE=${GENFACET_EXECUTABLE}")
+
+    set(generatedFiles
+        ${GF_OUTPUT_HPP_DIR}/${FACET}.hpp
+        ${GF_OUTPUT_HPP_DIR}/${GF_OUTPUT_IMPL_SUBDIR}/I${FACET}_D${REPR}.hpp
+        ${GF_OUTPUT_CPP_DIR}/I${FACET}_D${REPR}.cpp)
+
+    # Build the genfacet command
+    add_custom_command(
+        OUTPUT ${generatedFiles}
+        COMMAND ${GENFACET_EXECUTABLE}
+            --input ${GF_INPUT}
+            --output-hpp ${GF_OUTPUT_HPP_DIR}
+            --output-impl-hpp ${GF_OUTPUT_IMPL_SUBDIR}
+            --output-cpp ${GF_OUTPUT_CPP_DIR}
+        DEPENDS ${GF_INPUT}
+        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+        COMMENT "Generating facet source files from ${GF_INPUT}"
+        VERBATIM
+    )
+
+    # Create a target for this generation
+    add_custom_target(${GF_TARGET} DEPENDS ${generatedFiles})
 endmacro()