diff --git a/0005-Port-to-assertj-3.18.1.patch b/0005-Port-to-assertj-3.18.1.patch
new file mode 100644
index 0000000..48f90a9
--- /dev/null
+++ b/0005-Port-to-assertj-3.18.1.patch
@@ -0,0 +1,25 @@
+From 756086b87081019f4ed1720bded0a92fc79a2794 Mon Sep 17 00:00:00 2001
+From: Marian Koncek <mkoncek@redhat.com>
+Date: Fri, 22 Jan 2021 16:51:55 +0100
+Subject: [PATCH] Port to assertj 3.18.1
+
+---
+ .../src/main/java/org/xmlunit/assertj/CustomAbstractAssert.java | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/xmlunit-assertj/src/main/java/org/xmlunit/assertj/CustomAbstractAssert.java b/xmlunit-assertj/src/main/java/org/xmlunit/assertj/CustomAbstractAssert.java
+index 4d56aa5..a6b27c4 100644
+--- a/xmlunit-assertj/src/main/java/org/xmlunit/assertj/CustomAbstractAssert.java
++++ b/xmlunit-assertj/src/main/java/org/xmlunit/assertj/CustomAbstractAssert.java
+@@ -58,7 +58,7 @@ abstract class CustomAbstractAssert<SELF extends CustomAbstractAssert<SELF, ACTU
+         assertionError.setStackTrace(newStackTrace);
+     }
+ 
+-    private boolean isElementOfCustomAssert(StackTraceElement stackTraceElement) {
++    protected boolean isElementOfCustomAssert(StackTraceElement stackTraceElement) {
+ 
+         Class<?> currentAssertClass = getClass();
+         while (currentAssertClass != AbstractAssert.class) {
+-- 
+2.29.2
+
diff --git a/xmlunit.spec b/xmlunit.spec
index 7ebf0dc..02152e6 100644
--- a/xmlunit.spec
+++ b/xmlunit.spec
@@ -11,6 +11,7 @@ Patch1:         0001-Disable-tests-requiring-network-access.patch
 Patch2:         0002-Port-to-hamcrest-2.1.patch
 Patch3:         0003-Fix-test-failure.patch
 Patch4:         0004-Drop-support-for-JAXB.patch
+Patch5:         0005-Port-to-assertj-3.18.1.patch
 
 BuildRequires:  maven-local
 BuildRequires:  mvn(junit:junit)
@@ -74,6 +75,8 @@ This package provides %{summary}.
 %patch3 -p1
 %patch4 -p1
 
+%patch5 -p1
+
 %pom_remove_plugin org.codehaus.mojo:buildnumber-maven-plugin
 %pom_remove_plugin :maven-assembly-plugin
 %pom_remove_plugin -r :maven-shade-plugin