diff --git a/pkg/api/vlabs/validate.go b/pkg/api/vlabs/validate.go
index bf5d293952..978a61cf4e 100644
--- a/pkg/api/vlabs/validate.go
+++ b/pkg/api/vlabs/validate.go
@@ -235,6 +235,10 @@ func (a *AgentPoolProfile) Validate(orchestratorType string) error {
 		return e
 	}
 
+	if e := validatePoolOSType(a.OSType); e != nil {
+		return e
+	}
+
 	// for Kubernetes, we don't support AgentPoolProfile.DNSPrefix
 	if orchestratorType == Kubernetes {
 		if e := validate.Var(a.DNSPrefix, "len=0"); e != nil {
@@ -490,9 +494,6 @@ func (a *Properties) Validate(isUpdate bool) error {
 			return fmt.Errorf("VirtualMachineScaleSets are not supported with Kubernetes since Kubernetes requires the ability to attach/detach disks.  To fix specify \"AvailabilityProfile\":\"%s\"", AvailabilitySet)
 		}
 		if agentPoolProfile.OSType == Windows {
-			if e := validate.Var(a.WindowsProfile, "required"); e != nil {
-				return fmt.Errorf("WindowsProfile must not be empty since agent pool '%s' specifies windows", agentPoolProfile.Name)
-			}
 			switch a.OrchestratorProfile.OrchestratorType {
 			case DCOS:
 			case Swarm:
@@ -521,8 +522,12 @@ func (a *Properties) Validate(isUpdate bool) error {
 			default:
 				return fmt.Errorf("Orchestrator %s does not support Windows", a.OrchestratorProfile.OrchestratorType)
 			}
-			if e := a.WindowsProfile.Validate(); e != nil {
-				return e
+			if a.WindowsProfile != nil {
+				if e := a.WindowsProfile.Validate(); e != nil {
+					return e
+				}
+			} else {
+				return fmt.Errorf("WindowsProfile is required when the cluster definition contains Windows agent pool(s)")
 			}
 		}
 	}
@@ -818,6 +823,13 @@ func validatePoolName(poolName string) error {
 	return nil
 }
 
+func validatePoolOSType(os OSType) error {
+	if os != Linux && os != Windows && os != "" {
+		return fmt.Errorf("AgentPoolProfile.osType must be either Linux or Windows")
+	}
+	return nil
+}
+
 func validateDNSName(dnsName string) error {
 	dnsNameRegex := `^([A-Za-z][A-Za-z0-9-]{1,43}[A-Za-z0-9])$`
 	re, err := regexp.Compile(dnsNameRegex)