diff --git a/2021-05/spring-28/spring-28-exercise/pom.xml b/2021-05/spring-28/spring-28-exercise/pom.xml
index 9dc53ace..b746bd95 100644
--- a/2021-05/spring-28/spring-28-exercise/pom.xml
+++ b/2021-05/spring-28/spring-28-exercise/pom.xml
@@ -11,7 +11,7 @@
     <parent>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-parent</artifactId>
-        <version>2.5.5</version>
+        <version>2.3.3</version>
     </parent>
 
     <properties>
diff --git a/2021-05/spring-28/spring-28-solution/pom.xml b/2021-05/spring-28/spring-28-solution/pom.xml
index 83e77e91..7efc7017 100644
--- a/2021-05/spring-28/spring-28-solution/pom.xml
+++ b/2021-05/spring-28/spring-28-solution/pom.xml
@@ -11,7 +11,7 @@
     <parent>
         <groupId>org.springframework.boot</groupId>
         <artifactId>spring-boot-starter-parent</artifactId>
-        <version>2.5.5</version>
+        <version>2.3.3</version>
     </parent>
 
     <properties>