diff --git a/src/lagrangian/cfdemParticle/subModels/forceModel/BeetstraDrag/BeetstraDrag.H b/src/lagrangian/cfdemParticle/subModels/forceModel/BeetstraDrag/BeetstraDrag.H
index eb466cc2..21245471 100644
--- a/src/lagrangian/cfdemParticle/subModels/forceModel/BeetstraDrag/BeetstraDrag.H
+++ b/src/lagrangian/cfdemParticle/subModels/forceModel/BeetstraDrag/BeetstraDrag.H
@@ -66,7 +66,7 @@ protected:
 
     mutable label maxTypeCG_;
 
-    scalarList typeCG_;
+    mutable scalarList typeCG_;
 
     mutable scalar scaleDia_;