diff --git a/prep_satellite/get_oco2.f90 b/prep_satellite/get_oco2.f90
index 8ea646a5259187e03236eba12c9fdb7335aa1e3c..487cd4f7a93e02c5798bd6bbf6489daf92a018d3 100644
--- a/prep_satellite/get_oco2.f90
+++ b/prep_satellite/get_oco2.f90
@@ -368,6 +368,7 @@ subroutine get_oco2(settings)
 
     ! calculate column prior convolved with averaging kernel (units ppbv)
     allocate( cakpri(maxretr), stat=ierr )
+    cakpri(:) = 0.
     do nm = 1, nretr
       do nl = 1, nlevel
         cakpri(nm) = cakpri(nm) + vdryair_out(nm,nl)*vapri_out(nm,nl)*cak_out(nm,nl)