diff --git a/modules/openapi-generator/src/main/resources/Java/libraries/feign/auth/OAuth.mustache b/modules/openapi-generator/src/main/resources/Java/libraries/feign/auth/OAuth.mustache
index 0ed92dbcae9..c0344c1113f 100644
--- a/modules/openapi-generator/src/main/resources/Java/libraries/feign/auth/OAuth.mustache
+++ b/modules/openapi-generator/src/main/resources/Java/libraries/feign/auth/OAuth.mustache
@@ -120,7 +120,7 @@ public class OAuth implements RequestInterceptor {
 
     public synchronized void setAccessToken(String accessToken, Long expiresIn) {
         this.accessToken = accessToken;
-        this.expirationTimeMillis = System.currentTimeMillis() + expiresIn * MILLIS_PER_SECOND;
+        this.expirationTimeMillis = expiresIn == null ? null : System.currentTimeMillis() + expiresIn * MILLIS_PER_SECOND;
     }
 
     public TokenRequestBuilder getTokenRequestBuilder() {
diff --git a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/auth/OAuth.java b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/auth/OAuth.java
index 25593a0784a..7a2a822415d 100644
--- a/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/auth/OAuth.java
+++ b/samples/client/petstore/java/feign/src/main/java/org/openapitools/client/auth/OAuth.java
@@ -112,7 +112,7 @@ public class OAuth implements RequestInterceptor {
 
     public synchronized void setAccessToken(String accessToken, Long expiresIn) {
         this.accessToken = accessToken;
-        this.expirationTimeMillis = System.currentTimeMillis() + expiresIn * MILLIS_PER_SECOND;
+        this.expirationTimeMillis = expiresIn == null ? null : System.currentTimeMillis() + expiresIn * MILLIS_PER_SECOND;
     }
 
     public TokenRequestBuilder getTokenRequestBuilder() {
diff --git a/samples/client/petstore/java/feign10x/src/main/java/org/openapitools/client/auth/OAuth.java b/samples/client/petstore/java/feign10x/src/main/java/org/openapitools/client/auth/OAuth.java
index 75c86a7d61b..2aacac3bc84 100644
--- a/samples/client/petstore/java/feign10x/src/main/java/org/openapitools/client/auth/OAuth.java
+++ b/samples/client/petstore/java/feign10x/src/main/java/org/openapitools/client/auth/OAuth.java
@@ -113,7 +113,7 @@ public class OAuth implements RequestInterceptor {
 
     public synchronized void setAccessToken(String accessToken, Long expiresIn) {
         this.accessToken = accessToken;
-        this.expirationTimeMillis = System.currentTimeMillis() + expiresIn * MILLIS_PER_SECOND;
+        this.expirationTimeMillis = expiresIn == null ? null : System.currentTimeMillis() + expiresIn * MILLIS_PER_SECOND;
     }
 
     public TokenRequestBuilder getTokenRequestBuilder() {