diff --git a/examples/gcmc/data.spce b/examples/gcmc/data.spce
index 03f10e290f..5459e23014 100644
--- a/examples/gcmc/data.spce
+++ b/examples/gcmc/data.spce
@@ -28,8 +28,8 @@ LAMMPS data file. CGCMM style. atom_style full generated by VMD/TopoTools v1.8 o
 
  Masses
 
- 1 1.007940 # 1
- 2 15.999400 # 2
+ 1 15.999400 # 1
+ 2 1.007940 # 2
 
  Atoms # full