diff --git a/vlib/v/gen/c/comptime.v b/vlib/v/gen/c/comptime.v
index d229af3daa..78ed3ff44c 100644
--- a/vlib/v/gen/c/comptime.v
+++ b/vlib/v/gen/c/comptime.v
@@ -591,7 +591,7 @@ fn (mut g Gen) comp_if_to_ifdef(name string, is_comptime_optional bool) ?string
 			return '__sun'
 		}
 		'haiku' {
-			return '__haiku__'
+			return '__HAIKU__'
 		}
 		//
 		'js' {