diff --git a/examples/SpectralMethod/20grains64x64x64.geom b/examples/SpectralMethod/20grains64x64x64.geom
index c703104d6..6622966e4 100644
--- a/examples/SpectralMethod/20grains64x64x64.geom
+++ b/examples/SpectralMethod/20grains64x64x64.geom
@@ -2,7 +2,7 @@
 grid	a 64	b 64	c 64
 size	x 1.000000	y 1.000000	z 1.000000
 origin	x 0.000000	y 0.000000	z 0.000000
-microstructures
+microstructures 20
 homogenization	1
 19 19  2  2  2  2  2  2  2  2  2  2  2  2  4  4  4  4  4  4  4  4  4  4  4  4  4  4  4  4  1  1  1  1 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 19 19 19 19 19 19 19 19 19 19 19
 19 19 19  2  2  2  2  2  2  2  2  2  4  4  4  4  4  4  4  4  4  4  4  4  4  4  4  4  4  1  1  1  1  1 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 19 19 19 19 19 19 19 19 19 19