diff --git a/core/src/test/java/org/apache/calcite/test/DiffRepository.java b/core/src/test/java/org/apache/calcite/test/DiffRepository.java
index 36593df..875e2dc 100644
--- a/core/src/test/java/org/apache/calcite/test/DiffRepository.java
+++ b/core/src/test/java/org/apache/calcite/test/DiffRepository.java
@@ -235,7 +235,7 @@
    * Expands a string containing one or more variables. (Currently only works
    * if there is one variable.)
    */
-  public synchronized String expand(String tag, String text) {
+  public String expand(String tag, String text) {
     if (text == null) {
       return null;
     } else if (text.startsWith("${")