diff --git a/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation/validation.go b/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation/validation.go
index 82e4e9d15dd..e44e7bb9943 100644
--- a/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation/validation.go
+++ b/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation/validation.go
@@ -55,8 +55,10 @@ func ValidateCustomResourceDefinition(obj *apiextensions.CustomResourceDefinitio
 		return ret
 	}
 
+	allowDefaults, rejectDefaultsReason := allowDefaults(requestGV, nil)
 	opts := validationOptions{
-		allowDefaults:                            allowDefaults(requestGV, nil),
+		allowDefaults:                            allowDefaults,
+		disallowDefaultsReason:                   rejectDefaultsReason,
 		requireRecognizedConversionReviewVersion: true,
 		requireImmutableNames:                    false,
 		requireOpenAPISchema:                     requireOpenAPISchema(requestGV, nil),
@@ -80,6 +82,8 @@ func ValidateCustomResourceDefinition(obj *apiextensions.CustomResourceDefinitio
 type validationOptions struct {
 	// allowDefaults permits the validation schema to contain default attributes
 	allowDefaults bool
+	// disallowDefaultsReason gives a reason as to why allowDefaults is false (for better user feedback)
+	disallowDefaultsReason string
 	// requireRecognizedConversionReviewVersion requires accepted webhook conversion versions to contain a recognized version
 	requireRecognizedConversionReviewVersion bool
 	// requireImmutableNames disables changing spec.names
@@ -102,8 +106,10 @@ type validationOptions struct {
 
 // ValidateCustomResourceDefinitionUpdate statically validates
 func ValidateCustomResourceDefinitionUpdate(obj, oldObj *apiextensions.CustomResourceDefinition, requestGV schema.GroupVersion) field.ErrorList {
+	allowDefaults, rejectDefaultsReason := allowDefaults(requestGV, &oldObj.Spec)
 	opts := validationOptions{
-		allowDefaults:                            allowDefaults(requestGV, &oldObj.Spec),
+		allowDefaults:                            allowDefaults,
+		disallowDefaultsReason:                   rejectDefaultsReason,
 		requireRecognizedConversionReviewVersion: oldObj.Spec.Conversion == nil || hasValidConversionReviewVersionOrEmpty(oldObj.Spec.Conversion.ConversionReviewVersions),
 		requireImmutableNames:                    apiextensions.IsCRDConditionTrue(oldObj, apiextensions.Established),
 		requireOpenAPISchema:                     requireOpenAPISchema(requestGV, &oldObj.Spec),
@@ -661,6 +667,7 @@ func validateCustomResourceDefinitionValidation(customResourceValidation *apiext
 
 		openAPIV3Schema := &specStandardValidatorV3{
 			allowDefaults:            opts.allowDefaults,
+			disallowDefaultsReason:   opts.disallowDefaultsReason,
 			requireValidPropertyType: opts.requireValidPropertyType,
 		}
 
@@ -1110,16 +1117,17 @@ func allVersionsSpecifyOpenAPISchema(spec *apiextensions.CustomResourceDefinitio
 	return true
 }
 
-// allowDefaults returns true if the defaulting feature is enabled and the request group version allows adding defaults
-func allowDefaults(requestGV schema.GroupVersion, oldCRDSpec *apiextensions.CustomResourceDefinitionSpec) bool {
+// allowDefaults returns true if the defaulting feature is enabled and the request group version allows adding defaults,
+// or false and a reason for the user if defaults are not allowed.
+func allowDefaults(requestGV schema.GroupVersion, oldCRDSpec *apiextensions.CustomResourceDefinitionSpec) (bool, string) {
 	if oldCRDSpec != nil && specHasDefaults(oldCRDSpec) {
 		// don't tighten validation on existing persisted data
-		return true
+		return true, ""
 	}
 	if requestGV == apiextensionsv1beta1.SchemeGroupVersion {
-		return false
+		return false, "(cannot set default values in apiextensions.k8s.io/v1beta1 CRDs, must use apiextensions.k8s.io/v1)"
 	}
-	return true
+	return true, ""
 }
 
 func specHasDefaults(spec *apiextensions.CustomResourceDefinitionSpec) bool {
diff --git a/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation/validation_test.go b/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation/validation_test.go
index d34cd045d59..7dc6a8fc2d9 100644
--- a/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation/validation_test.go
+++ b/staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation/validation_test.go
@@ -38,6 +38,7 @@ import (
 type validationMatch struct {
 	path      *field.Path
 	errorType field.ErrorType
+	contains  string
 }
 
 func required(path ...string) validationMatch {
@@ -58,9 +59,12 @@ func immutable(path ...string) validationMatch {
 func forbidden(path ...string) validationMatch {
 	return validationMatch{path: field.NewPath(path[0], path[1:]...), errorType: field.ErrorTypeForbidden}
 }
+func forbiddenContains(contains string, path ...string) validationMatch {
+	return validationMatch{path: field.NewPath(path[0], path[1:]...), errorType: field.ErrorTypeForbidden, contains: contains}
+}
 
 func (v validationMatch) matches(err *field.Error) bool {
-	return err.Type == v.errorType && err.Field == v.path.String()
+	return err.Type == v.errorType && err.Field == v.path.String() && strings.Contains(err.Error(), v.contains)
 }
 
 func strPtr(s string) *string { return &s }
@@ -1641,7 +1645,7 @@ func TestValidateCustomResourceDefinition(t *testing.T) {
 			},
 			requestGV: apiextensionsv1beta1.SchemeGroupVersion,
 			errors: []validationMatch{
-				forbidden("spec", "validation", "openAPIV3Schema", "properties[a]", "default"), // disallowed via v1beta1
+				forbiddenContains("cannot set default values in apiextensions.k8s.io/v1beta1", "spec", "validation", "openAPIV3Schema", "properties[a]", "default"), // disallowed via v1beta1
 			},
 		},
 		{