diff --git a/include/valijson/constraints/concrete_constraints.hpp b/include/valijson/constraints/concrete_constraints.hpp
index b4df95e..9e67c19 100644
--- a/include/valijson/constraints/concrete_constraints.hpp
+++ b/include/valijson/constraints/concrete_constraints.hpp
@@ -914,9 +914,10 @@ public:
             freeFn(ptr);
             throw;
         }
+#else
+        // pretend to use freeFn to avoid warning in GCC 8.3
+        (void)freeFn;
 #endif
-
-	(void)freeFn;
     }
 
     virtual bool validate(const adapters::Adapter &target,