diff --git a/library/Makefile b/library/Makefile
index 9054ff8..0a023a3 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -89,6 +89,8 @@
 		threading.o	timing.o			\
 		xtea.o
 
+# For files generated by the parent project (Mbed TLS) when building Mbed
+# Crypto as a submodule, ensure that the parent project instance is used.
 ifdef USE_CRYPTO_SUBMODULE
 OBJS_CRYPTO += ../../library/error.o
 OBJS_CRYPTO += ../../library/version.o