diff --git a/internal/config/config.go b/internal/config/config.go
index c24115022..4cd99bf9d 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -70,7 +70,7 @@ type Config struct {
 	StateDiskSizeGB int `yaml:"stateDiskSizeGB" validate:"min=0"`
 	// description: |
 	//   Kubernetes version to be installed into the cluster.
-	KubernetesVersion string `yaml:"kubernetesVersion" validate:"supported_k8s_version"`
+	KubernetesVersion string `yaml:"kubernetesVersion" validate:"required,supported_k8s_version"`
 	// description: |
 	//   Microservice version to be installed into the cluster. Setting this value is optional until v2.7. Defaults to the version of the CLI.
 	MicroserviceVersion string `yaml:"microserviceVersion" validate:"omitempty,version_compatibility"`
@@ -543,7 +543,7 @@ func (c *Config) Validate(force bool) error {
 	}
 
 	// register custom validator with label supported_k8s_version to validate version based on available versionConfigs.
-	if err := validate.RegisterValidation("supported_k8s_version", validateK8sVersion); err != nil {
+	if err := validate.RegisterValidation("supported_k8s_version", c.validateK8sVersion); err != nil {
 		return err
 	}
 
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index 0629feb4f..0ea4bb33d 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -273,6 +273,26 @@ func TestValidate(t *testing.T) {
 				return cnf
 			}(),
 		},
+		// TODO: v2.7: remove this test as it should start breaking after v2.6 is released.
+		"k8s vMAJOR.MINOR is valid in v2.7": {
+			cnf: func() *Config {
+				cnf := Default()
+				cnf.KubernetesVersion = "v1.25"
+				return cnf
+			}(),
+			wantErr:      true,
+			wantErrCount: defaultErrCount,
+		},
+		// TODO: v2.7: remove this test as it should start breaking after v2.6 is released.
+		"k8s MAJOR.MINOR is valid in v2.7": {
+			cnf: func() *Config {
+				cnf := Default()
+				cnf.KubernetesVersion = "1.25"
+				return cnf
+			}(),
+			wantErr:      true,
+			wantErrCount: defaultErrCount,
+		},
 	}
 
 	for name, tc := range testCases {
diff --git a/internal/config/validation.go b/internal/config/validation.go
index caa166c56..fb863a1d5 100644
--- a/internal/config/validation.go
+++ b/internal/config/validation.go
@@ -311,8 +311,27 @@ func getPlaceholderEntries(m Measurements) []uint32 {
 	return placeholders
 }
 
-func validateK8sVersion(fl validator.FieldLevel) bool {
-	return versions.IsSupportedK8sVersion(compatibility.EnsurePrefixV(fl.Field().String()))
+func (c *Config) validateK8sVersion(fl validator.FieldLevel) bool {
+	// TODO: v2.7: do not create extendedVersion variable and directly validate field from fl.
+	// This patch is for compatibility with configs from v2.5 only. Configs specifying k8s
+	// the version as MAJOR.MINOR automatically get extended with the respective patch version.
+	configVersion := compatibility.EnsurePrefixV(fl.Field().String())
+	if !semver.IsValid(configVersion) {
+		return false
+	}
+	var extendedVersion string
+	switch semver.MajorMinor(configVersion) {
+	case semver.MajorMinor(string(versions.V1_24)):
+		extendedVersion = string(versions.V1_24)
+	case semver.MajorMinor(string(versions.V1_25)):
+		extendedVersion = string(versions.V1_25)
+	case semver.MajorMinor(string(versions.V1_26)):
+		extendedVersion = string(versions.V1_26)
+	default:
+		return false
+	}
+	c.KubernetesVersion = extendedVersion
+	return versions.IsSupportedK8sVersion(extendedVersion)
 }
 
 func registerVersionCompatibilityError(ut ut.Translator) error {