diff --git a/src/systems/include/mp-units/systems/angular.h b/src/systems/include/mp-units/systems/angular.h
index 41e30bb9..50cd3d5d 100644
--- a/src/systems/include/mp-units/systems/angular.h
+++ b/src/systems/include/mp-units/systems/angular.h
@@ -22,6 +22,8 @@
 
 #pragma once
 
+#include <mp-units/bits/hacks.h>
+
 // IWYU pragma: begin_exports
 #if MP_UNITS_HOSTED
 #include <mp-units/systems/angular/math.h>
diff --git a/src/systems/include/mp-units/systems/si.h b/src/systems/include/mp-units/systems/si.h
index 95f9fc87..b9d15db9 100644
--- a/src/systems/include/mp-units/systems/si.h
+++ b/src/systems/include/mp-units/systems/si.h
@@ -22,6 +22,8 @@
 
 #pragma once
 
+#include <mp-units/bits/hacks.h>
+
 // IWYU pragma: begin_exports
 #if MP_UNITS_HOSTED
 #include <mp-units/systems/si/chrono.h>