diff --git a/modules/openapi-generator/src/main/resources/r/modelAnyOf.mustache b/modules/openapi-generator/src/main/resources/r/modelAnyOf.mustache
index 287264a1ceb..d3b86f23ee8 100644
--- a/modules/openapi-generator/src/main/resources/r/modelAnyOf.mustache
+++ b/modules/openapi-generator/src/main/resources/r/modelAnyOf.mustache
@@ -47,6 +47,18 @@
       } else {
         NULL
       }
+    },
+    validateJSON = function(input) {
+      # backup current values
+      actual_instance_bak <- self$actual_instance
+      actual_type_bak <- self$actual_type
+
+      # if it's not valid, an error will be thrown
+      self$fromJSON(input)
+
+      # no error thrown, restore old values
+      self$actual_instance <- actual_instance_bak
+      self$actual_type <- actual_type_bak
     }
   )
 )
diff --git a/modules/openapi-generator/src/main/resources/r/modelOneOf.mustache b/modules/openapi-generator/src/main/resources/r/modelOneOf.mustache
index a4f92eee806..1e33da9e7ed 100644
--- a/modules/openapi-generator/src/main/resources/r/modelOneOf.mustache
+++ b/modules/openapi-generator/src/main/resources/r/modelOneOf.mustache
@@ -62,6 +62,18 @@
       } else {
         NULL
       }
+    },
+    validateJSON = function(input) {
+      # backup current values
+      actual_instance_bak <- self$actual_instance
+      actual_type_bak <- self$actual_type
+
+      # if it's not valid, an error will be thrown
+      self$fromJSON(input)
+
+      # no error thrown, restore old values
+      self$actual_instance <- actual_instance_bak
+      self$actual_type <- actual_type_bak
     }
   )
 )
diff --git a/samples/client/petstore/R/R/any_of_pig.R b/samples/client/petstore/R/R/any_of_pig.R
index 7197d52b438..d4e5fffe068 100644
--- a/samples/client/petstore/R/R/any_of_pig.R
+++ b/samples/client/petstore/R/R/any_of_pig.R
@@ -66,6 +66,18 @@ AnyOfPig <- R6::R6Class(
       } else {
         NULL
       }
+    },
+    validateJSON = function(input) {
+      # backup current values
+      actual_instance_bak <- self$actual_instance
+      actual_type_bak <- self$actual_type
+
+      # if it's not valid, an error will be thrown
+      self$fromJSON(input)
+
+      # no error thrown, restore old values
+      self$actual_instance <- actual_instance_bak
+      self$actual_type <- actual_type_bak
     }
   )
 )
diff --git a/samples/client/petstore/R/R/pig.R b/samples/client/petstore/R/R/pig.R
index e41f8834161..5afa7dc8943 100644
--- a/samples/client/petstore/R/R/pig.R
+++ b/samples/client/petstore/R/R/pig.R
@@ -82,6 +82,18 @@ Pig <- R6::R6Class(
       } else {
         NULL
       }
+    },
+    validateJSON = function(input) {
+      # backup current values
+      actual_instance_bak <- self$actual_instance
+      actual_type_bak <- self$actual_type
+
+      # if it's not valid, an error will be thrown
+      self$fromJSON(input)
+
+      # no error thrown, restore old values
+      self$actual_instance <- actual_instance_bak
+      self$actual_type <- actual_type_bak
     }
   )
 )
diff --git a/samples/client/petstore/R/tests/testthat/test_petstore.R b/samples/client/petstore/R/tests/testthat/test_petstore.R
index bb3df6fd168..a3481c4805c 100644
--- a/samples/client/petstore/R/tests/testthat/test_petstore.R
+++ b/samples/client/petstore/R/tests/testthat/test_petstore.R
@@ -159,6 +159,7 @@ test_that("Tests oneOf", {
   # test fromJSON, actual_tpye, actual_instance
   pig <- Pig$new()
   danish_pig <- pig$fromJSON(danish_pig_json)
+  pig$validateJSON(basque_pig_json) # validate JSON to ensure its actual_instance, actual_type are not updated
   expect_equal(danish_pig$actual_type, "DanishPig")
   expect_equal(danish_pig$actual_instance$size, 7)
   expect_equal(danish_pig$actual_instance$className, "DanishPig")
@@ -178,7 +179,7 @@ test_that("Tests oneOf", {
 
   # test exception when no matche found
   expect_error(pig$fromJSON('{}'), 'No match found when deserializing the payload into Pig with oneOf schemas BasquePig, DanishPig. Details:  The JSON input ` \\{\\} ` is invalid for BasquePig: the required field `className` is missing\\., The JSON input ` \\{\\} ` is invalid for DanishPig: the required field `className` is missing\\.')
-
+  expect_error(pig$validateJSON('{}'), 'No match found when deserializing the payload into Pig with oneOf schemas BasquePig, DanishPig. Details:  The JSON input ` \\{\\} ` is invalid for BasquePig: the required field `className` is missing\\., The JSON input ` \\{\\} ` is invalid for DanishPig: the required field `className` is missing\\.')
 
 })
 
@@ -221,7 +222,7 @@ test_that("Tests anyOf", {
 
   # test exception when no matche found
   expect_error(pig$fromJSON('{}'), 'No match found when deserializing the payload into AnyOfPig with anyOf schemas BasquePig, DanishPig. Details:  The JSON input ` \\{\\} ` is invalid for BasquePig: the required field `className` is missing\\., The JSON input ` \\{\\} ` is invalid for DanishPig: the required field `className` is missing\\.')
-
+  expect_error(pig$validateJSON('{}'), 'No match found when deserializing the payload into AnyOfPig with anyOf schemas BasquePig, DanishPig. Details:  The JSON input ` \\{\\} ` is invalid for BasquePig: the required field `className` is missing\\., The JSON input ` \\{\\} ` is invalid for DanishPig: the required field `className` is missing\\.')
 
 })