diff --git a/singularity/Singularity b/singularity/Singularity
index 610c3d29911551d2686701d4dfc8323904cdc709..584c643d5c1b6898ae4cac18f4243f9cd4f5467c 100644
--- a/singularity/Singularity
+++ b/singularity/Singularity
@@ -83,7 +83,8 @@ virtualenv --system-site-packages $VIRTUALENV_DIR
 # INSTALL REQUIRED PYTHON PACKAGES
 ##################################
 pip install jupyter==1.0.0 \
-            nglview==1.1.6
+            nglview==1.1.6 \
+            six==1.13.0
 
 # DOWNLOAD AND INSTALL MSMS
 ##############