diff --git a/libtomcrypt/Makefile.in b/libtomcrypt/Makefile.in
index ecc1ce678d31d549c43b0eb8177ed66ceb180b75..14bce99e853d9574eaa9c7d02124609c13c99a2c 100644
--- a/libtomcrypt/Makefile.in
+++ b/libtomcrypt/Makefile.in
@@ -19,7 +19,7 @@ srcdir=@srcdir@
 
 # Compilation flags. Note the += does not write over the user's CFLAGS!
 # The rest of the flags come from the parent Dropbear makefile
-CFLAGS += -c -I$(srcdir)/src/headers/ -I$(srcdir)/../
+CFLAGS += -c -I$(srcdir)/src/headers/ -I$(srcdir)/../ -DLTC_SOURCE
 
 # additional warnings (newer GCC 3.4 and higher)
 ifdef GCC_34