diff --git a/util/internal/test/src/main/java/org/hibernate/search/util/impl/test/rule/log4j/LogChecker.java b/util/internal/test/src/main/java/org/hibernate/search/util/impl/test/rule/log4j/LogChecker.java
index 775fe6a85b9..768d21a0b9a 100644
--- a/util/internal/test/src/main/java/org/hibernate/search/util/impl/test/rule/log4j/LogChecker.java
+++ b/util/internal/test/src/main/java/org/hibernate/search/util/impl/test/rule/log4j/LogChecker.java
@@ -43,7 +43,8 @@ public void appendFailure(Description description, String newline) {
 		}
 	}
 
-	void process(LogEvent event) {
+	// This must be synchronized to avoid problems when multiple threads issue log events concurrently
+	synchronized void process(LogEvent event) {
 		if ( expectation.getMaxExpectedCount() == null && expectation.getMinExpectedCount() <= count ) {
 			// We don't care about events anymore, expectations are met and it won't change
 			return;