diff --git a/packages/sak-meldinger/src/components/Messages.tsx b/packages/sak-meldinger/src/components/Messages.tsx
index 56170734f1..8f4c6b1a19 100644
--- a/packages/sak-meldinger/src/components/Messages.tsx
+++ b/packages/sak-meldinger/src/components/Messages.tsx
@@ -97,20 +97,29 @@ const createValidateRecipient = recipients => value =>
     ? undefined
     : [{ id: 'ValidationMessage.InvalidRecipient' }];
 
-const createTredjepartsmottaker = (orgnr: string): Mottaker => ({
-  id: orgnr,
-  type: "ORGNR",
-})
+const createTredjepartsmottaker = (orgnr: string): Mottaker => {
+  if (orgnr.length < 9) {
+    throw new Error(`Invalid orgnr: ${orgnr}`)
+  }
+  return {
+    id: orgnr,
+      type: "ORGNR",
+  }
+}
 
 const resolveOverstyrtMottaker = (
   overstyrtMottaker: string,
   recipients: Mottaker[],
   visTredjepartsmottaker: boolean,
-  tredjepartsmottakerOrgnr: string | undefined
+  tredjepartsmottakerOrgnr: string | undefined,
+  eregLookupResponse: EregOrganizationLookupResponse,
 ): Mottaker | undefined => {
   // Viss sending til tredjepartsmottaker er valgt skal tredjepartsmottakerOrgnr brukast (viss gyldig)
-  if (visTredjepartsmottaker && typeof tredjepartsmottakerOrgnr === "string" && tredjepartsmottakerOrgnr.length === 9) {
-    return createTredjepartsmottaker(tredjepartsmottakerOrgnr);
+  if (visTredjepartsmottaker) {
+    if(typeof tredjepartsmottakerOrgnr === "string" && tredjepartsmottakerOrgnr.length >= 9 && eregLookupResponse.name !== undefined) {
+      return createTredjepartsmottaker(tredjepartsmottakerOrgnr);
+    }
+    return undefined; // Tredjepartsmottaker aktivert, men ikkje funne gyldig
   }
   if (recipients.some(recipient => JSON.stringify(recipient) === overstyrtMottaker)) {
       return JSON.parse(overstyrtMottaker)
@@ -161,15 +170,19 @@ export const MessagesImpl = ({
 
   const tmpls: Brevmal[] = Object.keys(templates).map(key => ({ ...templates[key], kode: key }));
 
+  const resolvedOverstyrtMottaker: Mottaker | undefined =
+    resolveOverstyrtMottaker(overstyrtMottaker, recipients, visTredjepartsmottakerInput, tredjepartsmottakerOrgnr, tredjepartsmottakerInfo)
+
   const previewMessage = e => {
     e?.preventDefault();
-
-    previewCallback(
-      resolveOverstyrtMottaker(overstyrtMottaker, recipients, visTredjepartsmottakerInput, tredjepartsmottakerOrgnr),
-      brevmalkode,
-      fritekst,
-      fritekstbrev,
-    );
+    if (resolvedOverstyrtMottaker !== undefined) { // Don't want to start preview before valid receiver is resolved.
+      previewCallback(
+        resolvedOverstyrtMottaker,
+        brevmalkode,
+        fritekst,
+        fritekstbrev,
+      );
+    }
   };
 
 
@@ -184,9 +197,9 @@ export const MessagesImpl = ({
   useEffect(() => {
     formProps.change(
       'overstyrtMottaker',
-      JSON.stringify(resolveOverstyrtMottaker(overstyrtMottaker, recipients, visTredjepartsmottakerInput, tredjepartsmottakerOrgnr))
+      resolvedOverstyrtMottaker ? JSON.stringify(resolvedOverstyrtMottaker) : undefined
     );
-  }, [overstyrtMottaker, recipients, visTredjepartsmottakerInput, tredjepartsmottakerOrgnr])
+  }, [resolvedOverstyrtMottaker])
 
   useEffect(() => {
     if (tredjepartsmottakerOrgnr?.length >= 9) {
@@ -360,7 +373,7 @@ export const MessagesImpl = ({
           )}
           <VerticalSpacer eightPx />
           <div className={styles.buttonRow}>
-            <Hovedknapp mini spinner={formProps.submitting} disabled={formProps.submitting} onClick={ariaCheck}>
+            <Hovedknapp mini spinner={formProps.submitting} disabled={resolvedOverstyrtMottaker === undefined || formProps.submitting} onClick={ariaCheck}>
               {intl.formatMessage({ id: 'Messages.Submit' })}
             </Hovedknapp>
             {brevmalkode && (
diff --git a/packages/sak-meldinger/src/components/OrgnrInputField.tsx b/packages/sak-meldinger/src/components/OrgnrInputField.tsx
index 682592fd30..ca7a6ecc42 100644
--- a/packages/sak-meldinger/src/components/OrgnrInputField.tsx
+++ b/packages/sak-meldinger/src/components/OrgnrInputField.tsx
@@ -13,7 +13,11 @@ const OrgnrInputField = ({name, label, error}: OrgnrInputProps) => {
   const validator = (value?: string) => value?.length !== 9 ? [{id: 'ValidationMessage.InvalidOrganisasjonsnummer'}]: undefined;
   // maxLength is more than 9 to allow users to paste in numbers containing some characters/spaces, and let the parser
   // strip those out, e.g. If a user pastes MVA 123 456 789, the component should accept it and convert it to 123456789.
-  return <InputField name={name} label={label} parse={parser} maxLength={19} validate={[validator]} feil={error}/>
+
+  // This conditionalErrorProp thing is a workaround since apparently passing feil={error} directly causes the InputField
+  // to not use the validator even when error is undefined.
+  const conditionalErrorProp = error ? {feil: error} : {}
+  return <InputField name={name} label={label} parse={parser} maxLength={19} validate={[validator]} {...conditionalErrorProp} />
 }
 
 export default OrgnrInputField;