diff --git a/clients/apps/web/src/components/Orders/DownloadInvoice.tsx b/clients/apps/web/src/components/Orders/DownloadInvoice.tsx
index d6c9d0ab3d..840fb77a30 100644
--- a/clients/apps/web/src/components/Orders/DownloadInvoice.tsx
+++ b/clients/apps/web/src/components/Orders/DownloadInvoice.tsx
@@ -341,6 +341,7 @@ const DownloadInvoice = ({
                           country={country}
                           value={field.value || ''}
                           onChange={field.onChange}
+                          disabled={order.paid}
                         />
                         <FormMessage />
                       </>
@@ -361,6 +362,7 @@ const DownloadInvoice = ({
                           value={field.value || undefined}
                           onChange={field.onChange}
                           allowedCountries={enums.addressInputCountryValues}
+                          disabled={order.paid}
                         />
                         <FormMessage />
                       </>
diff --git a/clients/packages/ui/src/components/atoms/CountryPicker.tsx b/clients/packages/ui/src/components/atoms/CountryPicker.tsx
index dc2d87866e..f1190ea744 100644
--- a/clients/packages/ui/src/components/atoms/CountryPicker.tsx
+++ b/clients/packages/ui/src/components/atoms/CountryPicker.tsx
@@ -28,6 +28,7 @@ const CountryPicker = ({
   className,
   itemClassName,
   contentClassName,
+  disabled,
 }: {
   allowedCountries: readonly string[]
   value?: string
@@ -36,11 +37,17 @@ const CountryPicker = ({
   className?: string
   itemClassName?: string
   contentClassName?: string
+  disabled?: boolean
 }) => {
   const countryMap = getCountryList(allowedCountries as TCountryCode[])
   return (
-    <Select onValueChange={onChange} value={value} autoComplete={autoComplete}>
-      <SelectTrigger className={className}>
+    <Select
+      onValueChange={onChange}
+      value={value}
+      autoComplete={autoComplete}
+      disabled={disabled}
+    >
+      <SelectTrigger className={className} disabled={disabled}>
         <SelectValue
           placeholder="Country"
           // Avoids issues due to browser automatic translation
diff --git a/clients/packages/ui/src/components/atoms/CountryStatePicker.tsx b/clients/packages/ui/src/components/atoms/CountryStatePicker.tsx
index fc1543970e..71438840f3 100644
--- a/clients/packages/ui/src/components/atoms/CountryStatePicker.tsx
+++ b/clients/packages/ui/src/components/atoms/CountryStatePicker.tsx
@@ -84,6 +84,7 @@ const CountryStatePicker = ({
   autoComplete,
   itemClassName,
   contentClassName,
+  disabled,
 }: {
   className?: string
   contentClassName?: string
@@ -92,6 +93,7 @@ const CountryStatePicker = ({
   onChange: (value: string) => void
   country?: string
   autoComplete?: string
+  disabled?: boolean
 }) => {
   if (country === 'US' || country === 'CA') {
     const states = country === 'US' ? US_STATES : CA_PROVINCES
@@ -100,8 +102,9 @@ const CountryStatePicker = ({
         onValueChange={onChange}
         value={value}
         autoComplete={autoComplete}
+        disabled={disabled}
       >
-        <SelectTrigger className={className}>
+        <SelectTrigger className={className} disabled={disabled}>
           <SelectValue
             placeholder={country === 'US' ? 'State' : 'Province'}
             // Avoids issues due to browser automatic translation
@@ -133,6 +136,7 @@ const CountryStatePicker = ({
       placeholder="State / Province"
       value={value}
       onChange={(e) => onChange(e.target.value)}
+      disabled={disabled}
     />
   )
 }
diff --git a/server/polar/order/service.py b/server/polar/order/service.py
index 66ce65da32..22d361ad9a 100644
--- a/server/polar/order/service.py
+++ b/server/polar/order/service.py
@@ -28,7 +28,7 @@
 from polar.event.service import event as event_service
 from polar.event.system import OrderPaidMetadata, SystemEvent, build_system_event
 from polar.eventstream.service import publish as eventstream_publish
-from polar.exceptions import PolarError
+from polar.exceptions import PolarError, PolarRequestValidationError
 from polar.file.s3 import S3_SERVICES
 from polar.held_balance.service import held_balance as held_balance_service
 from polar.integrations.stripe.service import stripe as stripe_service
@@ -339,6 +339,42 @@ async def update(
         order: Order,
         order_update: OrderUpdate | CustomerOrderUpdate,
     ) -> Order:
+        # Validate that country/state cannot be changed after order is paid
+        # because VAT was calculated based on the original address
+        if order.paid and order_update.billing_address is not None:
+            new_address = order_update.billing_address
+            existing_address = order.billing_address
+
+            new_country = str(new_address.country) if new_address else None
+            new_state = new_address.state if new_address else None
+            existing_country = (
+                str(existing_address.country) if existing_address else None
+            )
+            existing_state = existing_address.state if existing_address else None
+
+            if new_country != existing_country:
+                raise PolarRequestValidationError(
+                    [
+                        {
+                            "type": "value_error",
+                            "loc": ("body", "billing_address", "country"),
+                            "msg": "Cannot change country after order is paid.",
+                            "input": new_country,
+                        }
+                    ]
+                )
+            if new_state != existing_state:
+                raise PolarRequestValidationError(
+                    [
+                        {
+                            "type": "value_error",
+                            "loc": ("body", "billing_address", "state"),
+                            "msg": "Cannot change state after order is paid.",
+                            "input": new_state,
+                        }
+                    ]
+                )
+
         repository = OrderRepository.from_session(session)
         order = await repository.update(
             order, update_dict=order_update.model_dump(exclude_unset=True)