diff --git a/index.html b/index.html
index 3f6060d6..f4896cb9 100644
--- a/index.html
+++ b/index.html
@@ -98,6 +98,7 @@ <h1 class="l--page">Tinker With a <b>Neural Network</b> <span class="optional">R
             <option value="tanh">Tanh</option>
             <option value="sigmoid">Sigmoid</option>
             <option value="linear">Linear</option>
+            <option value="sine">Sine</option>
           </select>
         </div>
       </div>
diff --git a/src/nn.ts b/src/nn.ts
index e92a13de..4e919491 100644
--- a/src/nn.ts
+++ b/src/nn.ts
@@ -134,6 +134,10 @@ export class Activations {
     output: x => x,
     der: x => 1
   };
+  public static SINE: ActivationFunction = {
+    output: x => (Math as any).sin(x),
+    der: x => (Math as any).cos(x)
+  };
 }
 
 /** Build-in regularization functions */
diff --git a/src/state.ts b/src/state.ts
index 42dc8154..bdb2ae69 100644
--- a/src/state.ts
+++ b/src/state.ts
@@ -24,7 +24,8 @@ export let activations: {[key: string]: nn.ActivationFunction} = {
   "relu": nn.Activations.RELU,
   "tanh": nn.Activations.TANH,
   "sigmoid": nn.Activations.SIGMOID,
-  "linear": nn.Activations.LINEAR
+  "linear": nn.Activations.LINEAR,
+  "sine": nn.Activations.SINE
 };
 
 /** A map between names and regularization functions. */