diff --git a/src/hydro_common.h b/src/hydro_common.h
index e14392d..195dbed 100644
--- a/src/hydro_common.h
+++ b/src/hydro_common.h
@@ -4,8 +4,7 @@
 namespace euler2d
 {
 
-#define NDIM 2
-#define NBVAR 4
+constexpr int NBVAR = 4;
 
 } // namespace euler2d