diff --git a/CMakeLists.txt b/CMakeLists.txt
index f9440a31..aae9d1df 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -96,6 +96,11 @@ else()
   find_package(g2c REQUIRED)
 endif()
 
+# Set a pre-processor symbol if we are using g2c API.
+if (USE_G2C_API)
+  add_definitions(-DG2C_API)
+endif()
+
 # Figure whether user wants a _4, a _d, or both libraries.
 if(BUILD_4 AND BUILD_D)
   set(kinds "4" "d")
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 12a0e0e0..fd60cc3e 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -9,7 +9,12 @@ g2grids.F90 g2get.F90 g2getgb2.F90 g2index.F90 g2gf.F90 g2unpack.F90
 g2create.F90 ${CMAKE_CURRENT_BINARY_DIR}/gribmod.F90 gridtemplates.F90
 intmath.F90 g2jpc.F90 pack_gp.f params_ecmwf.F90 params.F90
 pdstemplates.F90 g2png.F90 realloc.F90 reduce.f g2sim.F90 skgb.F90
-g2spec.F90 g2logging.F90 g2cf.F90 g2c_interface.F90)
+g2spec.F90 g2logging.F90)
+
+# Add the G2C API code if required.
+if (USE_G2C_API)
+  set(fortran_src ${fortran_src} g2cf.F90 g2c_interface.F90)
+endif()
 
 # This function calls NCEPLIBS-w3emc.
 if (BUILD_WITH_W3EMC)