diff --git a/src/main/org/apache/tools/ant/Project.java b/src/main/org/apache/tools/ant/Project.java
index d56f36d15..ef89ffc89 100644
--- a/src/main/org/apache/tools/ant/Project.java
+++ b/src/main/org/apache/tools/ant/Project.java
@@ -910,7 +910,9 @@ public class Project implements ResourceFactory {
         while (e.hasMoreElements()) {
             String propertyName = (String) e.nextElement();
             String value = systemP.getProperty(propertyName);
-            this.setPropertyInternal(propertyName, value);
+            if (value != null) {
+                this.setPropertyInternal(propertyName, value);
+            }
         }
     }