diff --git a/pipeline.py b/pipeline.py
index c1c5719..6f28eac 100644
--- a/pipeline.py
+++ b/pipeline.py
@@ -253,7 +253,10 @@ class Components :
 							# 			skip_columns.append(_name)
 				if x_cols :
 					for _col in x_cols :
-						_df[_col] = self.approximate(df[_col].fillna(-1))
+						if df[_col].unique().size > 0 :
+							_df[_col] = self.approximate(df[_col].fillna(-1))
+						else:
+							_df[_col] = -1
 				#
 				# We perform a series of set operations to insure that the following conditions are met:
 				#	- the synthetic dataset only has fields that need to be synthesized