diff --git a/src/org/easymock/internal/EasyMockProperties.java b/src/org/easymock/internal/EasyMockProperties.java
index 5094104..5043095 100644
--- a/src/org/easymock/internal/EasyMockProperties.java
+++ b/src/org/easymock/internal/EasyMockProperties.java
@@ -73,8 +73,8 @@
             }
         }
         // Then overload it with system properties
-        for (Map.Entry<Object, Object> entry : System.getProperties()
-                .entrySet()) {
+        for (Map.Entry<Object, Object> entry : ((Properties)System.getProperties()
+                 .clone()).entrySet()) {
             if (entry.getKey() instanceof String
                     && entry.getKey().toString().startsWith(PREFIX)) {
                 properties.put(entry.getKey(), entry.getValue());