diff --git a/fslstats.cc b/fslstats.cc
index 65548ccd481bc1ec3b3a6a5fcda2b21484ac6da9..130ab1aeb06a12383be0c4943c86f46acb09cc05 100644
--- a/fslstats.cc
+++ b/fslstats.cc
@@ -312,7 +312,7 @@ int fmrib_main_float(int argc, char* argv[])
       generate_masks(mask,masknz,vin,lthr,uthr);
       vol = vin * mask;
     } else if (sarg=="-a") {
-      vol = abs(vin);
+      vol = abs(vol);
     } else if (sarg=="-v") {
       if (masks_used) {
 	cout << (long int) mask.sum() << " "