diff --git a/pmd-core/src/main/java/net/sourceforge/pmd/cpd/GUI.java b/pmd-core/src/main/java/net/sourceforge/pmd/cpd/GUI.java
index c51770960f..3424466dd2 100644
--- a/pmd-core/src/main/java/net/sourceforge/pmd/cpd/GUI.java
+++ b/pmd-core/src/main/java/net/sourceforge/pmd/cpd/GUI.java
@@ -631,7 +631,7 @@ public class GUI implements CPDListener {
             int separatorPos = sourceId.lastIndexOf(File.separatorChar);
             label = "..." + sourceId.substring(separatorPos);
         } else {
-            label = '(' + sourceIDs.size() + " separate files)";
+            label = '(' + String.valueOf(sourceIDs.size()) + " separate files)";
         }
 
         match.setLabel(label);