diff --git a/src/event/spec.ts b/src/event/spec.ts
index 25def7df..bfab4f3d 100644
--- a/src/event/spec.ts
+++ b/src/event/spec.ts
@@ -18,10 +18,11 @@ export function validateCloudEvent<T>(event: CloudEventV1<T>): boolean {
   } else {
     return false;
   }
-  // attribute names must all be lowercase
+  // attribute names must all be [a-z|0-9]
+  const validation = /^[a-z0-9]+$/;
   for (const key in event) {
-    if (key !== key.toLowerCase()) {
-      throw new ValidationError(`invalid attribute name: ${key}`);
+    if (validation.test(key) === false && key !== "data_base64") {
+      throw new ValidationError(`invalid attribute name: "${key}"`);
     }
   }
   return true;
diff --git a/test/integration/kafka_tests.ts b/test/integration/kafka_tests.ts
index 8870d479..ac0e0c47 100644
--- a/test/integration/kafka_tests.ts
+++ b/test/integration/kafka_tests.ts
@@ -131,7 +131,7 @@ describe("Kafka transport", () => {
     expect(event.LUNCH).to.equal("tacos");
     expect(function () {
       event.validate();
-    }).to.throw("invalid attribute name: LUNCH");
+    }).to.throw("invalid attribute name: \"LUNCH\"");
   });
 
   it("Can detect CloudEvent binary Messages with weird versions", () => {
diff --git a/test/integration/message_test.ts b/test/integration/message_test.ts
index b1afad4b..46ab21f0 100644
--- a/test/integration/message_test.ts
+++ b/test/integration/message_test.ts
@@ -41,7 +41,21 @@ const imageData = new Uint32Array(fs.readFileSync(path.join(process.cwd(), "test
 const image_base64 = asBase64(imageData);
 
 describe("HTTP transport", () => {
-  
+  it("validates extension attribute names for incoming messages", () => {
+    // create a new Message
+    const msg: Message = {
+      headers: {
+        "ce-id": "213",
+        "ce-source": "test",
+        "ce-type": "test",
+        "ce-bad-extension": "value"
+      },
+      body: undefined
+    };
+    const evt = HTTP.toEvent(msg) as CloudEvent;
+    expect(() => evt.validate()).to.throw(TypeError);
+  });
+
   it("Includes extensions in binary mode when type is 'boolean' with a false value", () => {
     const evt = new CloudEvent({ source: "test", type: "test", extboolean: false });
     expect(evt.hasOwnProperty("extboolean")).to.equal(true);
@@ -129,7 +143,7 @@ describe("HTTP transport", () => {
     expect(event.LUNCH).to.equal("tacos");
     expect(function () {
       event.validate();
-    }).to.throw("invalid attribute name: LUNCH");
+    }).to.throw("invalid attribute name: \"LUNCH\"");
   });
 
   it("Can detect CloudEvent binary Messages with weird versions", () => {
diff --git a/test/integration/mqtt_tests.ts b/test/integration/mqtt_tests.ts
index 411a9cd7..69b77e52 100644
--- a/test/integration/mqtt_tests.ts
+++ b/test/integration/mqtt_tests.ts
@@ -134,7 +134,7 @@ describe("MQTT transport", () => {
     expect(event.LUNCH).to.equal("tacos");
     expect(function () {
       event.validate();
-    }).to.throw("invalid attribute name: LUNCH");
+    }).to.throw("invalid attribute name: \"LUNCH\"");
   });
 
   it("Can detect CloudEvent binary Messages with weird versions", () => {
diff --git a/test/integration/spec_1_tests.ts b/test/integration/spec_1_tests.ts
index 7bd22483..9759d8fc 100644
--- a/test/integration/spec_1_tests.ts
+++ b/test/integration/spec_1_tests.ts
@@ -99,6 +99,16 @@ describe("CloudEvents Spec v1.0", () => {
     it("should be ok when the type is an string converted from an object", () => {
       expect(cloudevent.cloneWith({ objectextension: JSON.stringify({ some: "object" }) }).validate()).to.equal(true);
     });
+
+    it("should only allow a-z|0-9 in the attribute names", () => {
+      const testCases = [
+        "an extension", "an_extension", "an-extension", "an.extension", "an+extension"
+      ];
+      testCases.forEach((testCase) => {
+        const evt = cloudevent.cloneWith({ [testCase]: "a value"}, false);
+        expect(() => evt.validate()).to.throw(ValidationError);
+      });
+    });
   });
 
   describe("The Constraints check", () => {