diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0210e26c..dbd636ef 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -42,9 +42,9 @@ include_directories(${INCDIR} ${MODDIR} ${LIBDIR})
 message(STATUS "Using IPK size: ${PSB_IPK_SIZE}")
 message(STATUS "Using LPK size: ${PSB_LPK_SIZE}")
 
-
-add_compile_options(-DPSB_IPK${PSB_IPK_SIZE})
-add_compile_options(-DPSB_LPK${PSB_LPK_SIZE})
+# Add PSB_IPK/LPK flag only for fortran files.
+set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS} -DPSB_IPK${IPK_SIZE}")
+set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS} -DPSB_LPK${LPK_SIZE}")