diff --git a/src/event/spec.ts b/src/event/spec.ts
index ec0bf07..1d308bb 100644
--- a/src/event/spec.ts
+++ b/src/event/spec.ts
@@ -28,14 +28,21 @@ export function validateCloudEvent(event: CloudEventV03 | CloudEventV1): boolean
     if (!isValidAgainstSchemaV1(event)) {
       throw new ValidationError("invalid payload", isValidAgainstSchemaV1.errors);
     }
-    return true;
   } else if (event.specversion === Version.V03) {
     if (!isValidAgainstSchemaV03(event)) {
       throw new ValidationError("invalid payload", isValidAgainstSchemaV03.errors);
     }
-    return checkDataContentEncoding(event);
+    checkDataContentEncoding(event);
+  } else {
+    return false;
   }
-  return false;
+  // attribute names must all be lowercase
+  for (const key in event) {
+    if (key !== key.toLowerCase()) {
+      throw new ValidationError(`invalid attribute name: ${key}`);
+    }
+  }
+  return true;
 }
 
 function checkDataContentEncoding(event: CloudEventV03): boolean {
diff --git a/src/event/validation.ts b/src/event/validation.ts
index ca43534..6279cce 100644
--- a/src/event/validation.ts
+++ b/src/event/validation.ts
@@ -19,7 +19,7 @@ export class ValidationError extends TypeError {
           // @ts-ignore
           errors?.reduce(
             (accum: string, err: Record<string, string>) =>
-              (accum as string).concat(`
+              accum.concat(`
   ${err instanceof Object ? JSON.stringify(err) : err}`),
             message,
           )
diff --git a/src/message/http/index.ts b/src/message/http/index.ts
index ad6356f..029965e 100644
--- a/src/message/http/index.ts
+++ b/src/message/http/index.ts
@@ -151,7 +151,7 @@ function getVersion(mode: Mode, headers: Headers, body: string | Record<string,
  * @throws {ValidationError} of the event does not conform to the spec
  */
 function parseBinary(message: Message, version: Version): CloudEvent {
-  const headers = message.headers;
+  const headers = { ...message.headers };
   let body = message.body;
 
   if (!headers) throw new ValidationError("headers is null or undefined");
@@ -167,11 +167,12 @@ function parseBinary(message: Message, version: Version): CloudEvent {
       const mappedParser: MappedParser = parserMap[header];
       eventObj[mappedParser.name] = mappedParser.parser.parse(sanitizedHeaders[header]);
       delete sanitizedHeaders[header];
+      delete headers[header];
     }
   }
 
   // Every unprocessed header can be an extension
-  for (const header in sanitizedHeaders) {
+  for (const header in headers) {
     if (header.startsWith(CONSTANTS.EXTENSIONS_PREFIX)) {
       eventObj[header.substring(CONSTANTS.EXTENSIONS_PREFIX.length)] = headers[header];
     }
diff --git a/test/integration/message_test.ts b/test/integration/message_test.ts
index 85169de..893686b 100644
--- a/test/integration/message_test.ts
+++ b/test/integration/message_test.ts
@@ -64,6 +64,26 @@ describe("HTTP transport", () => {
     expect(HTTP.isEvent(message)).to.be.true;
   });
 
+  it("Respects extension attribute casing (even if against spec)", () => {
+    // Now create a message that is an event
+    const message = {
+      body: `{ "greeting": "hello" }`,
+      headers: {
+        [CONSTANTS.CE_HEADERS.ID]: "1234",
+        [CONSTANTS.CE_HEADERS.SOURCE]: "test",
+        [CONSTANTS.CE_HEADERS.TYPE]: "test.event",
+        [CONSTANTS.CE_HEADERS.SPEC_VERSION]: Version.V1,
+        "ce-LUNCH": "tacos",
+      },
+    };
+    expect(HTTP.isEvent(message)).to.be.true;
+    const event: CloudEvent = HTTP.toEvent(message);
+    expect(event.LUNCH).to.equal("tacos");
+    expect(function () {
+      event.validate();
+    }).to.throw("invalid attribute name: LUNCH");
+  });
+
   it("Can detect CloudEvent binary Messages with weird versions", () => {
     // Now create a message that is an event
     const message = {