diff --git a/src/napi.rs b/src/napi.rs
index 6d22cb5..b708d41 100644
--- a/src/napi.rs
+++ b/src/napi.rs
@@ -262,8 +262,11 @@ impl Headers {
     /// ```
     #[napi]
     pub fn get(&self, key: String) -> Option<String> {
+        // Return the last value for this key (HTTP headers can have multiple values)
         self.0
-            .get(&key)
+            .get_all(&key)
+            .iter()
+            .last()
             .and_then(|v| v.to_str().map(|s| s.to_string()).ok())
     }
 
@@ -431,7 +434,7 @@ impl Headers {
     /// ```
     #[napi(getter)]
     pub fn size(&self) -> u32 {
-        self.0.len() as u32
+        self.0.keys_len() as u32
     }
 
     /// Get an iterator over the header entries.
diff --git a/test/headers.test.mjs b/test/headers.test.mjs
index eaa675d..ae23e79 100644
--- a/test/headers.test.mjs
+++ b/test/headers.test.mjs
@@ -50,7 +50,7 @@ test('Headers', async t => {
       baz: ['buz', 'bux']
     })
     strictEqual(headers.get('foo'), 'bar', 'should return the value of an existing header')
-    deepStrictEqual(headers.get('baz'), 'buz', 'should return first value for a multi-value header')
+    deepStrictEqual(headers.get('baz'), 'bux', 'should return last value for a multi-value header')
     strictEqual(headers.get('not-exists'), null, 'should return null for non-existing header')
   })
 
@@ -108,13 +108,13 @@ test('Headers', async t => {
       foo: 'bar',
       baz: ['buz', 'bux']
     })
-    strictEqual(headers.size, 3, 'should have correct size with multiple headers')
+    strictEqual(headers.size, 2, 'should count unique header keys')
     headers.set('foo', 'new-value')
-    strictEqual(headers.size, 3, 'should not change size when replacing a header value')
+    strictEqual(headers.size, 2, 'should not change size when replacing a header value')
     headers.add('new-header', 'value')
-    strictEqual(headers.size, 4, 'should increase size when adding a new header')
+    strictEqual(headers.size, 3, 'should increase size when adding a new header')
     headers.add('baz', 'new-baz-value')
-    strictEqual(headers.size, 5, 'should increase size when adding a new value to an existing header')
+    strictEqual(headers.size, 3, 'should not increase size when adding a new value to an existing header')
     headers.clear()
     strictEqual(headers.size, 0, 'should be zero after clearing headers')
   })