diff --git a/src/SecExp/js/secExp.js b/src/SecExp/js/secExp.js
index dd93f42c1e435e80f07488b98e3cdcfe175715a9..ea6650e9a572ec7cb61a39e51650a6d734eed9e2 100644
--- a/src/SecExp/js/secExp.js
+++ b/src/SecExp/js/secExp.js
@@ -861,7 +861,7 @@ App.SecExp.Check = (function() {
 			V.SecExp.buildings.propHub.active = V.SecExp.buildings.propHub.active || 0;
 			if (jsDef(V.SecExp.buildings.pr)) {
 				V.SecExp.buildings.propHub = V.SecExp.buildings.pr;
-				V.SecExp.buildings.pr = null;
+				delete V.SecExp.buildings.pr;
 			}
 			if (jsDef(V.propHub)) {
 				V.SecExp.buildings.propHub.active = V.propHub; delete V.propHub;