diff --git a/src/main/org/apache/tools/ant/ComponentHelper.java b/src/main/org/apache/tools/ant/ComponentHelper.java
index e7cc4d6c2..c81f88857 100644
--- a/src/main/org/apache/tools/ant/ComponentHelper.java
+++ b/src/main/org/apache/tools/ant/ComponentHelper.java
@@ -806,7 +806,7 @@ public class ComponentHelper  {
      * called for each component name, check if the
      * associated URI has been examined for antlibs.
      */
-    private void checkNamespace(String componentName) {
+    private synchronized void checkNamespace(String componentName) {
         if (componentName.indexOf(':') == -1) {
             return; // not a namespaced name
         }