diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 4b07f355a..f5947088e 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -18,6 +18,15 @@ target_sources(POETLib
   Chemistry/SurrogateModels/ProximityHashTable.cpp
 )
 
+set(POET_TUG_APPROACH "Implicit" CACHE STRING "tug numerical approach to use")
+set_property(CACHE POET_TUG_APPROACH PROPERTY STRINGS "Implicit" "Explicit")
+
+if (POET_TUG_APPROACH STREQUAL "Implicit")
+  target_compile_definitions(POETLib PRIVATE POET_TUG_BTCS)
+elseif (POET_TUG_APPROACH STREQUAL "Explicit")
+  target_compile_definitions(POETLib PRIVATE POET_TUG_FTCS)
+endif()
+
 target_include_directories(POETLib PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}")
 target_link_libraries(
   POETLib 
diff --git a/src/Transport/DiffusionModule.cpp b/src/Transport/DiffusionModule.cpp
index 754d135c9..d7f1df5f3 100644
--- a/src/Transport/DiffusionModule.cpp
+++ b/src/Transport/DiffusionModule.cpp
@@ -81,7 +81,14 @@ void DiffusionModule::simulate(double requested_dt) {
 
   grid.setDomain(param_list.s_rows, param_list.s_cols);
 
+#if defined(POET_TUG_BTCS)
   tug::Simulation<TugType> sim(grid, boundary);
+#elif defined(POET_TUG_FTCS)
+  tug::Simulation<TugType, tug::FTCS_APPROACH> sim(grid, boundary);
+#else
+#error "No valid approach defined"
+#endif
+
   sim.setIterations(1);
 
   for (const auto &sol_name : this->param_list.transport_names) {