diff --git a/src/include/units/prefix.h b/src/include/units/prefix.h
index fbf45665..129be0b3 100644
--- a/src/include/units/prefix.h
+++ b/src/include/units/prefix.h
@@ -23,6 +23,7 @@
 #pragma once
 
 #include <units/bits/external/downcasting.h>
+#include <units/concepts.h>
 #include <units/ratio.h>
 #include <units/symbol_text.h>
 
diff --git a/src/include/units/quantity_cast.h b/src/include/units/quantity_cast.h
index 14bfbd5b..42f3118b 100644
--- a/src/include/units/quantity_cast.h
+++ b/src/include/units/quantity_cast.h
@@ -26,6 +26,8 @@
 #include <units/customization_points.h>
 #include <units/bits/dimension_op.h>
 #include <units/bits/external/type_traits.h>
+#include <units/quantity.h>
+#include <units/quantity_point.h>
 #include <cassert>
 
 #ifdef _MSC_VER