diff --git a/doc/CMakeLists.txt b/doc/CMakeLists.txt
index c2ccb2749a80..0294c950a40c 100644
--- a/doc/CMakeLists.txt
+++ b/doc/CMakeLists.txt
@@ -5,24 +5,30 @@
 #==============================================================================
 
 find_package(Doxygen)
-  if (PIO_ENABLE_ASYNC)
-    SET(C_SRC_FILES "@CMAKE_CURRENT_SOURCE_DIR@/../src/clib/bget.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pioc.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pioc_sc.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_darray_async.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_get_nc_async.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_internal.h @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_nc4.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_put_nc_async.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_spmd.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/bget.h @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pioc_support.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_lists.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_nc_async.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_varm.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/dtypes.h  @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_file.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio.h @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_msg.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_rearrange.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/topology.c")
-  else ()
-    SET(C_SRC_FILES "@CMAKE_CURRENT_SOURCE_DIR@/../src/clib/bget.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pioc.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pioc_sc.c  @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_internal.h @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_nc4.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_spmd.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/bget.h @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pioc_support.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_darray.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_get_nc.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_lists.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_put_nc.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_varm.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/dtypes.h @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_file.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio.h @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_msg.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_nc.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_rearrange.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/topology.c")
-  endif ()
 
-  if(DOXYGEN_FOUND)
+# This supports the build with/witout async code. Once async code is
+# fully merged, remove the definition of C_SRC_FILES and its mention
+# in Doxyfile.in for simplicity.
+if (PIO_ENABLE_ASYNC)
+  SET(C_SRC_FILES "@CMAKE_CURRENT_SOURCE_DIR@/../src/clib/bget.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pioc.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pioc_sc.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_darray_async.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_get_nc_async.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_internal.h @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_nc4.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_put_nc_async.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_spmd.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/bget.h @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pioc_support.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_lists.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_nc_async.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_varm.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/dtypes.h  @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_file.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio.h @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_msg.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_rearrange.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/topology.c")
+else ()
+  SET(C_SRC_FILES "@CMAKE_CURRENT_SOURCE_DIR@/../src/clib/bget.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pioc.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pioc_sc.c  @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_internal.h @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_nc4.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_spmd.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/bget.h @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pioc_support.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_darray.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_get_nc.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_lists.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_put_nc.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_varm.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/dtypes.h @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_file.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio.h @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_msg.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_nc.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/pio_rearrange.c @CMAKE_CURRENT_SOURCE_DIR@/../src/clib/topology.c")
+endif ()
 
-    configure_file(${CMAKE_CURRENT_SOURCE_DIR}/Doxyfile.in 
-                   ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile @ONLY)
-    add_custom_target(doc
-        COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_SOURCE_DIR}/customdoxygen.css 
-                                         ${CMAKE_CURRENT_BINARY_DIR}
-        COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_SOURCE_DIR}/DoxygenLayout.xml 
-                                         ${CMAKE_CURRENT_BINARY_DIR}
-        COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_SOURCE_DIR}/doxygen.sty 
-                                         ${CMAKE_CURRENT_BINARY_DIR}
-        COMMAND ${DOXYGEN_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
-        WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
-        COMMENT "Generating API documentation with Doxygen" VERBATIM)
+if(DOXYGEN_FOUND)
+  # Process the Doxyfile using options set during configure.
+  configure_file(${CMAKE_CURRENT_SOURCE_DIR}/Doxyfile.in 
+    ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile @ONLY)
+
+  # Copy necessary files.
+  add_custom_target(doc
+    COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_SOURCE_DIR}/customdoxygen.css 
+    ${CMAKE_CURRENT_BINARY_DIR}
+    COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_SOURCE_DIR}/DoxygenLayout.xml 
+    ${CMAKE_CURRENT_BINARY_DIR}
+    COMMAND ${CMAKE_COMMAND} -E copy ${CMAKE_CURRENT_SOURCE_DIR}/doxygen.sty 
+    ${CMAKE_CURRENT_BINARY_DIR}
+    COMMAND ${DOXYGEN_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
+    WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+    COMMENT "Generating API documentation with Doxygen" VERBATIM)
 endif(DOXYGEN_FOUND)