diff --git a/Makefile.in b/Makefile.in
index 391fb71..3741599 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -565,6 +565,7 @@
 lib_LTLIBRARIES = libndn-c.la libndn-cpp.la
 
 # Public C headers.
+# NOTE: If a new directory is added, then add it to ndn_cpp_c_headers in include/Makefile.am.
 ndn_cpp_c_headers = \
   include/ndn-cpp/ndn-cpp-config.h \
   include/ndn-cpp/c/common.h \
@@ -576,6 +577,7 @@
 
 
 # Public C++ headers.
+# NOTE: If a new directory is added, then add it to ndn_cpp_cpp_headers in include/Makefile.am.
 ndn_cpp_cpp_headers = \
   include/ndn-cpp/common.hpp \
   include/ndn-cpp/data.hpp \