diff --git a/modules/openapi-generator/src/main/resources/ruby-client/partial_anyof_module.mustache b/modules/openapi-generator/src/main/resources/ruby-client/partial_anyof_module.mustache
index 778568c2c31c..f979fdd3100e 100644
--- a/modules/openapi-generator/src/main/resources/ruby-client/partial_anyof_module.mustache
+++ b/modules/openapi-generator/src/main/resources/ruby-client/partial_anyof_module.mustache
@@ -56,7 +56,7 @@
         when 'Time'
           return Time.parse(data)
         when 'Date'
-          return Date.parse(data)
+          return Date.iso8601(data)
         when 'String'
           return data if data.instance_of?(String)
         when 'Object' # "type: object"
diff --git a/modules/openapi-generator/src/main/resources/ruby-client/partial_oneof_module.mustache b/modules/openapi-generator/src/main/resources/ruby-client/partial_oneof_module.mustache
index d3a25f69ed5e..8dd7b381d2bd 100644
--- a/modules/openapi-generator/src/main/resources/ruby-client/partial_oneof_module.mustache
+++ b/modules/openapi-generator/src/main/resources/ruby-client/partial_oneof_module.mustache
@@ -98,7 +98,7 @@
         when 'Time'
           return Time.parse(data)
         when 'Date'
-          return Date.parse(data)
+          return Date.iso8601(data)
         when 'String'
           return data if data.instance_of?(String)
         when 'Object' # "type: object"
diff --git a/samples/client/petstore/ruby-httpx/lib/petstore/models/mammal_anyof.rb b/samples/client/petstore/ruby-httpx/lib/petstore/models/mammal_anyof.rb
index e15e001c7ccd..c5ef0a052ce6 100644
--- a/samples/client/petstore/ruby-httpx/lib/petstore/models/mammal_anyof.rb
+++ b/samples/client/petstore/ruby-httpx/lib/petstore/models/mammal_anyof.rb
@@ -64,7 +64,7 @@ def find_and_cast_into_type(klass, data)
         when 'Time'
           return Time.parse(data)
         when 'Date'
-          return Date.parse(data)
+          return Date.iso8601(data)
         when 'String'
           return data if data.instance_of?(String)
         when 'Object' # "type: object"
diff --git a/samples/client/petstore/ruby-httpx/lib/petstore/models/mammal_without_discriminator.rb b/samples/client/petstore/ruby-httpx/lib/petstore/models/mammal_without_discriminator.rb
index 7c37e6492dd6..9042380114e5 100644
--- a/samples/client/petstore/ruby-httpx/lib/petstore/models/mammal_without_discriminator.rb
+++ b/samples/client/petstore/ruby-httpx/lib/petstore/models/mammal_without_discriminator.rb
@@ -65,7 +65,7 @@ def find_and_cast_into_type(klass, data)
         when 'Time'
           return Time.parse(data)
         when 'Date'
-          return Date.parse(data)
+          return Date.iso8601(data)
         when 'String'
           return data if data.instance_of?(String)
         when 'Object' # "type: object"
diff --git a/samples/client/petstore/ruby/lib/petstore/models/mammal_anyof.rb b/samples/client/petstore/ruby/lib/petstore/models/mammal_anyof.rb
index e15e001c7ccd..c5ef0a052ce6 100644
--- a/samples/client/petstore/ruby/lib/petstore/models/mammal_anyof.rb
+++ b/samples/client/petstore/ruby/lib/petstore/models/mammal_anyof.rb
@@ -64,7 +64,7 @@ def find_and_cast_into_type(klass, data)
         when 'Time'
           return Time.parse(data)
         when 'Date'
-          return Date.parse(data)
+          return Date.iso8601(data)
         when 'String'
           return data if data.instance_of?(String)
         when 'Object' # "type: object"
diff --git a/samples/client/petstore/ruby/lib/petstore/models/mammal_without_discriminator.rb b/samples/client/petstore/ruby/lib/petstore/models/mammal_without_discriminator.rb
index 7c37e6492dd6..9042380114e5 100644
--- a/samples/client/petstore/ruby/lib/petstore/models/mammal_without_discriminator.rb
+++ b/samples/client/petstore/ruby/lib/petstore/models/mammal_without_discriminator.rb
@@ -65,7 +65,7 @@ def find_and_cast_into_type(klass, data)
         when 'Time'
           return Time.parse(data)
         when 'Date'
-          return Date.parse(data)
+          return Date.iso8601(data)
         when 'String'
           return data if data.instance_of?(String)
         when 'Object' # "type: object"