diff --git a/plugins/junit5_rt_tests/test/com/intellij/junit5/JUnitVersionSwitchingIntegrationTest.java b/plugins/junit5_rt_tests/test/com/intellij/junit5/JUnitVersionSwitchingIntegrationTest.java
index 6e5ecd6a3296..e8102981f2f0 100644
--- a/plugins/junit5_rt_tests/test/com/intellij/junit5/JUnitVersionSwitchingIntegrationTest.java
+++ b/plugins/junit5_rt_tests/test/com/intellij/junit5/JUnitVersionSwitchingIntegrationTest.java
@@ -111,7 +111,9 @@ public class JUnitVersionSwitchingIntegrationTest extends AbstractTestFrameworkC
 
     ProcessOutput output = doStartTestsProcess(configuration,
                                                params -> replaceJUnitVersion(params, JUnitStarter.JUNIT6_PARAMETER));
-    assertEmpty(output.err);
+
+    assertTrue("stderr must contain the 'JUnit 6 cannot be used with the current test runtime classpath. Falling back to JUnit 5.' error message",
+               ContainerUtil.exists(output.err, s -> s.contains("JUnit 6 cannot be used with the current test runtime classpath. Falling back to JUnit 5.")));
 
     assertTrue(output.sys.toString().contains("-junit6"));
     assertTrue("Test output must report that JUnit6 classes are absent (junit6.classes.present=false)",
@@ -152,7 +154,9 @@ public class JUnitVersionSwitchingIntegrationTest extends AbstractTestFrameworkC
     assertNotNull(configuration);
 
     ProcessOutput output = doStartTestsProcess(configuration, params -> replaceJUnitVersion(params, JUnitStarter.JUNIT6_PARAMETER));
-    assertEmpty(output.err);
+
+    assertTrue("stderr must contain the 'JUnit 6 cannot be used with the current test runtime classpath. Falling back to JUnit 5.' error message",
+               ContainerUtil.exists(output.err, s -> s.contains("JUnit 6 cannot be used with the current test runtime classpath. Falling back to JUnit 5.")));
 
     assertTrue(output.sys.toString().contains("-junit6"));
     assertTrue("Test output must report that JUnit6 classes are absent (junit6.classes.present=false)",
diff --git a/plugins/junit_rt/src/com/intellij/rt/junit/JUnitStarter.java b/plugins/junit_rt/src/com/intellij/rt/junit/JUnitStarter.java
index 2d54be8d91f7..465e3814ebf6 100644
--- a/plugins/junit_rt/src/com/intellij/rt/junit/JUnitStarter.java
+++ b/plugins/junit_rt/src/com/intellij/rt/junit/JUnitStarter.java
@@ -157,6 +157,15 @@ public final class JUnitStarter {
     switch (runner) {
       case JUNIT6:
         if (JUnitRunner.JUNIT6.check()) return JUnitRunner.JUNIT6;
+        if (JUnitRunner.JUNIT5.check()) {
+          System.err.println("JUnit 6 cannot be used with the current test runtime classpath. Falling back to JUnit 5.");
+          System.err.println("If you expected JUnit 6, please check the test runtime dependencies.");
+          System.err.flush();
+          return JUnitRunner.JUNIT5;
+        }
+        System.err.println("!!! JUnit Platform is not available on the classpath");
+        System.err.flush();
+        System.exit(-3);
       case JUNIT5:
         if (JUnitRunner.JUNIT5.check()) return JUnitRunner.JUNIT5;
         System.err.println("!!! JUnit Platform is not available on the classpath");