diff --git a/definitions/mars/grib.mmsf.fc.def b/definitions/mars/grib.mmsf.fc.def
index 7adb27059..f1820336a 100644
--- a/definitions/mars/grib.mmsf.fc.def
+++ b/definitions/mars/grib.mmsf.fc.def
@@ -1,4 +1,9 @@
-alias mars.step   = endStep;
+if (levtype is "o2d" || levtype is "o3d") {
+   alias mars.step = stepRange;
+} else {
+   alias mars.step = endStep;
+}
+
 if (class is "od") { alias mars.system = systemNumber; }
 if (class is "me") { alias mars.system = systemNumber; }
 if (class is "en") { alias mars.system = systemNumber; }
@@ -18,8 +23,3 @@ if (centre == 80 && subCentre == 98 && class is "c3") {
 
 if (class is "ci") { unalias mars.method; }
 
-if (levtype is "o2d" || levtype is "o3d") {
-   alias mars.step = stepRange;
-} else {
-   alias mars.step = endStep;
-}