diff --git a/core/src/main/java/org/springframework/security/authentication/AbstractUserDetailsReactiveAuthenticationManager.java b/core/src/main/java/org/springframework/security/authentication/AbstractUserDetailsReactiveAuthenticationManager.java
index 13712c7a683..f7a392c4e5d 100644
--- a/core/src/main/java/org/springframework/security/authentication/AbstractUserDetailsReactiveAuthenticationManager.java
+++ b/core/src/main/java/org/springframework/security/authentication/AbstractUserDetailsReactiveAuthenticationManager.java
@@ -184,7 +184,7 @@ public void setUserDetailsPasswordService(ReactiveUserDetailsPasswordService use
 	 * @since 5.2
 	 */
 	public void setPostAuthenticationChecks(UserDetailsChecker postAuthenticationChecks) {
-		Assert.notNull(this.postAuthenticationChecks, "postAuthenticationChecks cannot be null");
+		Assert.notNull(postAuthenticationChecks, "postAuthenticationChecks cannot be null");
 		this.postAuthenticationChecks = postAuthenticationChecks;
 	}
 
diff --git a/core/src/test/java/org/springframework/security/authentication/UserDetailsRepositoryReactiveAuthenticationManagerTests.java b/core/src/test/java/org/springframework/security/authentication/UserDetailsRepositoryReactiveAuthenticationManagerTests.java
index e77f145479b..0f9b62e71a8 100644
--- a/core/src/test/java/org/springframework/security/authentication/UserDetailsRepositoryReactiveAuthenticationManagerTests.java
+++ b/core/src/test/java/org/springframework/security/authentication/UserDetailsRepositoryReactiveAuthenticationManagerTests.java
@@ -90,6 +90,12 @@ public void setSchedulerWhenNullThenIllegalArgumentException() {
 		assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> this.manager.setScheduler(null));
 	}
 
+	@Test
+	public void setPostAuthenticationChecksWhenNullThenIllegalArgumentException() {
+		assertThatExceptionOfType(IllegalArgumentException.class)
+			.isThrownBy(() -> this.manager.setPostAuthenticationChecks(null));
+	}
+
 	@Test
 	public void authenticateWhenCustomSchedulerThenUsed() {
 		given(this.scheduler.schedule(any())).willAnswer((a) -> {