diff --git a/src/compute_vcm_chunk.cpp b/src/compute_vcm_chunk.cpp
index 0fcb22ce12..dd2c075653 100644
--- a/src/compute_vcm_chunk.cpp
+++ b/src/compute_vcm_chunk.cpp
@@ -88,8 +88,8 @@ void ComputeVCMChunk::setup()
   // done in setup, so that ComputeChunkAtom::setup() is already called
 
   if (firstflag && cchunk->idsflag == ONCE) {
-    firstflag = massneed = 0;
     compute_array();
+    firstflag = massneed = 0;
   }
 }