diff --git a/lsmtool/operations/group.py b/lsmtool/operations/group.py
index 41d7cb20f43944b9c90425c3a9af5e75a3f3ba44..c0c262f8a58ba68641c1baf6d1ee17e77954b77f 100644
--- a/lsmtool/operations/group.py
+++ b/lsmtool/operations/group.py
@@ -260,7 +260,8 @@ def group(LSM, algorithm, targetFlux=None, weightBySize=False, numClusters=100,
             if weightBySize:
                 sizes = LSM.getPatchSizes(units='arcsec', weight=True, applyBeam=applyBeam)
                 sizes[sizes < 1.0] = 1.0
-                medianSize = np.median(sizes)
+                bright_ind = np.where(fluxes >= targetFlux)
+                medianSize = np.median(sizes[bright_ind])
                 weights = medianSize / sizes
                 weights[weights > 1.0] = 1.0
                 weights[weights < 0.5] = 0.5