diff --git a/modules/openapi-generator/src/main/resources/cpp-rest-sdk-client/modelbase-source.mustache b/modules/openapi-generator/src/main/resources/cpp-rest-sdk-client/modelbase-source.mustache
index faa2333603a..160f6ce89de 100644
--- a/modules/openapi-generator/src/main/resources/cpp-rest-sdk-client/modelbase-source.mustache
+++ b/modules/openapi-generator/src/main/resources/cpp-rest-sdk-client/modelbase-source.mustache
@@ -264,7 +264,7 @@ bool ModelBase::fromJson( const web::json::value& val, int32_t & outVal )
 }
 bool ModelBase::fromJson( const web::json::value& val, int64_t & outVal )
 {
-    outVal = !val.is_null() ? std::numeric_limits<int64_t>::quiet_NaN() : val.as_number().to_int64();
+    outVal = !val.is_number() ? std::numeric_limits<int64_t>::quiet_NaN() : val.as_number().to_int64();
     return val.is_number();
 }
 bool ModelBase::fromJson( const web::json::value& val, utility::string_t & outVal )
diff --git a/samples/client/petstore/cpp-restsdk/client/ModelBase.cpp b/samples/client/petstore/cpp-restsdk/client/ModelBase.cpp
index 7807662a936..97f2120f35d 100644
--- a/samples/client/petstore/cpp-restsdk/client/ModelBase.cpp
+++ b/samples/client/petstore/cpp-restsdk/client/ModelBase.cpp
@@ -275,7 +275,7 @@ bool ModelBase::fromJson( const web::json::value& val, int32_t & outVal )
 }
 bool ModelBase::fromJson( const web::json::value& val, int64_t & outVal )
 {
-    outVal = !val.is_null() ? std::numeric_limits<int64_t>::quiet_NaN() : val.as_number().to_int64();
+    outVal = !val.is_number() ? std::numeric_limits<int64_t>::quiet_NaN() : val.as_number().to_int64();
     return val.is_number();
 }
 bool ModelBase::fromJson( const web::json::value& val, utility::string_t & outVal )