diff --git a/processing/legacy/geom_grainGrowth.py b/processing/legacy/geom_grainGrowth.py
index 23a46b668..d969b415c 100755
--- a/processing/legacy/geom_grainGrowth.py
+++ b/processing/legacy/geom_grainGrowth.py
@@ -28,6 +28,7 @@ Smoothen interface roughness by simulated curvature flow.
 This is achieved by the diffusion of each initially sharply bounded grain volume within the periodic domain
 up to a given distance 'd' voxels.
 The final geometry is assembled by selecting at each voxel that grain index for which the concentration remains largest.
+References 10.1073/pnas.1111557108 (10.1006/jcph.1994.1105)
 
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