diff --git a/PROMS/Volian.Controls.Library/DisplayTransition.cs b/PROMS/Volian.Controls.Library/DisplayTransition.cs
index 2f37a327..de78501e 100644
--- a/PROMS/Volian.Controls.Library/DisplayTransition.cs
+++ b/PROMS/Volian.Controls.Library/DisplayTransition.cs
@@ -1199,6 +1199,13 @@ namespace Volian.Controls.Library
 					"Cannot add recusive transition", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
 				return;
 			}
+			// B2015-170 - don't allow a transition to step that is not sequental
+			if ((toItem != null &&!toItem.IsNumbered) || (rangeItem != null && !rangeItem.IsNumbered))
+			{
+				MessageBox.Show("For transitions containing step references, the transition must be to a numbered or lettered step.",
+					"Cannot add transition to a non-seqential step", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
+				return;
+			}
 			bool doTranmod = cbPageNum.Visible && cbPageNum.Checked;
 			trantxt = TransitionText.GetResolvedText(MyRTB.MyItemInfo, listBoxTranFmt.SelectedIndex, toItem, rangeItem ?? toItem, doTranmod);
 			int ss = MyRTB.SelectionStart;// Remember where the link is being added