diff --git a/cas/src/main/java/org/springframework/security/cas/jackson/package-info.java b/cas/src/main/java/org/springframework/security/cas/jackson/package-info.java
index 261d47c9b5..2e2c39b848 100644
--- a/cas/src/main/java/org/springframework/security/cas/jackson/package-info.java
+++ b/cas/src/main/java/org/springframework/security/cas/jackson/package-info.java
@@ -17,4 +17,7 @@
 /**
  * Jackson 3+ serialization support for CAS.
  */
+@NullMarked
 package org.springframework.security.cas.jackson;
+
+import org.jspecify.annotations.NullMarked;
diff --git a/web/src/main/java/org/springframework/security/web/jackson/DefaultSavedRequestMixin.java b/web/src/main/java/org/springframework/security/web/jackson/DefaultSavedRequestMixin.java
index f9eee79ee3..61a52e47a4 100644
--- a/web/src/main/java/org/springframework/security/web/jackson/DefaultSavedRequestMixin.java
+++ b/web/src/main/java/org/springframework/security/web/jackson/DefaultSavedRequestMixin.java
@@ -19,6 +19,7 @@ package org.springframework.security.web.jackson;
 import com.fasterxml.jackson.annotation.JsonAutoDetect;
 import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.annotation.JsonTypeInfo;
+import org.jspecify.annotations.Nullable;
 import tools.jackson.databind.annotation.JsonDeserialize;
 
 import org.springframework.security.web.savedrequest.DefaultSavedRequest;
@@ -40,6 +41,6 @@ import org.springframework.security.web.savedrequest.DefaultSavedRequest;
 abstract class DefaultSavedRequestMixin {
 
 	@JsonInclude(JsonInclude.Include.NON_NULL)
-	String matchingRequestParameterName;
+	@Nullable String matchingRequestParameterName;
 
 }
diff --git a/web/src/main/java/org/springframework/security/web/jackson/package-info.java b/web/src/main/java/org/springframework/security/web/jackson/package-info.java
index 1e5c3c1d49..a325c3c7a2 100644
--- a/web/src/main/java/org/springframework/security/web/jackson/package-info.java
+++ b/web/src/main/java/org/springframework/security/web/jackson/package-info.java
@@ -17,4 +17,7 @@
 /**
  * Jackson 3+ serialization support for web.
  */
+@NullMarked
 package org.springframework.security.web.jackson;
+
+import org.jspecify.annotations.NullMarked;