diff --git a/dlib/optimization.h b/dlib/optimization.h
index 839749d80..439bcb82a 100644
--- a/dlib/optimization.h
+++ b/dlib/optimization.h
@@ -8,6 +8,7 @@
 #include "optimization/optimization_solve_qp_using_smo.h"
 #include "optimization/optimization_oca.h"
 #include "optimization/optimization_trust_region.h"
+#include "optimization/optimization_least_squares.h"
 
 #endif // DLIB_OPTIMIZATIOn_HEADER