diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1e1f2c8f..8cc851a1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -810,6 +810,10 @@ CONFIGURE_FILE("${CMAKE_SOURCE_DIR}/CTestConfig.cmake.in"
   "${CMAKE_SOURCE_DIR}/CTestConfig.cmake"
   @ONLY)
 
+# Fortran compiler flag for the (module) include directory. Used for generating nf-config.
+SET(MOD_FLAG -I)
+
+
 # Generate nf-config form template.
 CONFIGURE_FILE("${CMAKE_SOURCE_DIR}/nf-config.cmake.in"
   "${CMAKE_BINARY_DIR}/tmp/nf-config" @ONLY