diff --git a/include/duckhandy/tiger_bt.hpp b/include/duckhandy/tiger_bt.hpp
index e94b45b..7c07bfc 100644
--- a/include/duckhandy/tiger_bt.hpp
+++ b/include/duckhandy/tiger_bt.hpp
@@ -18,6 +18,7 @@
 #ifndef id1E6CCE44307549A9B6C9E4E5923AC002
 #define id1E6CCE44307549A9B6C9E4E5923AC002
 
+#include "lengthof.h"
 #include <cstdint>
 #include <ciso646>
 #include <climits>
diff --git a/include/duckhandy/tiger_bt.inl b/include/duckhandy/tiger_bt.inl
index 4cfbb89..c982962 100644
--- a/include/duckhandy/tiger_bt.inl
+++ b/include/duckhandy/tiger_bt.inl
@@ -15,11 +15,6 @@
  * along with "duckhandy".  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#ifndef lengthof
-#	define lengthof(a) (sizeof(a) / sizeof((a)[0]))
-#	define UNDEF_lengthof
-#endif
-
 namespace dhandy::bt {
 	namespace implem {
 		constexpr const uint64_t table[4*256] = {0x02AAB17CF7E90C5EULL, 0xAC424B03E243A8ECULL,
@@ -491,8 +486,3 @@ namespace dhandy::bt {
 		);
 	}
 } //namespace dhandy::bt
-
-#if defined UNDEF_lengthof
-#	undef lengthof
-#	undef UNDEF_lengthof
-#endif