diff --git a/src/core/include/units/ratio.h b/src/core/include/units/ratio.h
index 52270e2d..c5e03d5c 100644
--- a/src/core/include/units/ratio.h
+++ b/src/core/include/units/ratio.h
@@ -32,6 +32,7 @@
 
 #include <gsl/gsl-lite.hpp>
 #include <array>
+#include <compare>
 #include <numeric>
 
 namespace units {