diff --git a/packages/oas-to-har/test/parameters.test.ts b/packages/oas-to-har/test/parameters.test.ts
index 497f86f4..a1617fe8 100644
--- a/packages/oas-to-har/test/parameters.test.ts
+++ b/packages/oas-to-har/test/parameters.test.ts
@@ -143,7 +143,7 @@ describe('parameter handling', () => {
     );
 
     it(
-      'should pass in value if one is set and prioritise provided values',
+      'should pass in value if one is set and prioritize provided values',
       assertQueryParams(
         {
           parameters: [{ name: 'a', in: 'query', required: true, schema: { default: 'value' } }],
@@ -401,7 +401,7 @@ describe('parameter handling', () => {
     );
 
     it(
-      'should pass in value if one is set and prioritise provided values',
+      'should pass in value if one is set and prioritize provided values',
       assertHeaders(
         {
           parameters: [{ name: 'a', in: 'header', required: true, schema: { default: 'value' } }],
@@ -411,6 +411,17 @@ describe('parameter handling', () => {
       ),
     );
 
+    it(
+      'should retain defined header casing',
+      assertHeaders(
+        {
+          parameters: [{ name: 'reqKey', in: 'header', required: true, schema: { default: 'value' } }],
+        },
+        { header: { reqKey: 'test' } },
+        [{ name: 'reqKey', value: 'test' }],
+      ),
+    );
+
     it(
       'should pass an `accept` header if endpoint expects a content back from response',
       assertHeaders(
diff --git a/packages/oas-to-har/test/requestBody.test.ts b/packages/oas-to-har/test/requestBody.test.ts
index 3de989af..185488a8 100644
--- a/packages/oas-to-har/test/requestBody.test.ts
+++ b/packages/oas-to-har/test/requestBody.test.ts
@@ -66,7 +66,7 @@ describe('request body handling', () => {
       expect(oasToHar(spec, spec.operation('/requestBody', 'post')).log.entries[0].request.postData).toBeUndefined();
     });
 
-    it('should pass in value if one is set and prioritise provided values', () => {
+    it('should pass in value if one is set and prioritize provided values', () => {
       const spec = Oas.init({
         paths: {
           '/requestBody': {
@@ -1070,7 +1070,7 @@ describe('request body handling', () => {
       expect(har.log.entries[0].request.postData).toBeUndefined();
     });
 
-    it('should pass in value if one is set and prioritise provided values', () => {
+    it('should pass in value if one is set and prioritize provided values', () => {
       const spec = Oas.init({
         paths: {
           '/requestBody': {
@@ -1206,7 +1206,7 @@ describe('request body handling', () => {
     });
 
     // Whether this is right or wrong, i'm not sure but this is what readme currently does
-    it('should prioritise json if it exists', async () => {
+    it('should prioritize json if it exists', async () => {
       const contentSpec = Oas.init({
         paths: {
           '/requestBody': {
diff --git a/packages/oas/test/operation.test.ts b/packages/oas/test/operation.test.ts
index 013d4611..63f97a07 100644
--- a/packages/oas/test/operation.test.ts
+++ b/packages/oas/test/operation.test.ts
@@ -166,7 +166,7 @@ describe('#getContentType()', () => {
     expect(petstore.operation('/pet', 'post').getContentType()).toBe('application/json');
   });
 
-  it('should prioritise json if it exists', () => {
+  it('should prioritize json if it exists', () => {
     expect(
       new Operation(petstore.getDefinition(), '/body', 'get', {
         requestBody: {