diff --git a/src/smt/old_interval.cpp b/src/smt/old_interval.cpp
index efdb78754..e719f7e2b 100644
--- a/src/smt/old_interval.cpp
+++ b/src/smt/old_interval.cpp
@@ -292,7 +292,7 @@ v_dependency * interval::join_opt(v_dependency * d1, v_dependency * d2, v_depend
 }
 
 interval & interval::operator*=(interval const & other) {
-#if Z3DEBUG || _TRACE
+#if defined(Z3DEBUG) || defined(_TRACE)
     bool contains_zero1 = contains_zero();
     bool contains_zero2 = other.contains_zero();
 #endif