diff --git a/include/SPECK3D_INT_ENC.h b/include/SPECK3D_INT_ENC.h
index 2b73fa67..2ccb25e2 100644
--- a/include/SPECK3D_INT_ENC.h
+++ b/include/SPECK3D_INT_ENC.h
@@ -3,8 +3,6 @@
 
 #include "SPECK3D_INT.h"
 
-#include <optional>
-
 namespace sperr {
 
 //