diff --git a/crates/viewer/src/camera.rs b/crates/viewer/src/camera.rs
index 6397ebf1..cf1af5e0 100644
--- a/crates/viewer/src/camera.rs
+++ b/crates/viewer/src/camera.rs
@@ -58,7 +58,9 @@ impl OrbitCamera {
     }
 
     /// Zoom in or out, while looking at the same target.
-    pub fn zoom(&mut self, zoom_delta: f32) {}
+    pub fn zoom(&mut self, zoom_delta: f32) {
+        self.radius = f32::max(self.radius * f32::exp(zoom_delta), f32::EPSILON);
+    }
 
     /// Orbit around the target while keeping the distance.
     pub fn rotate(&mut self, rotator: Quat) {
diff --git a/crates/viewer/src/main.rs b/crates/viewer/src/main.rs
index 4993d70c..e00211a1 100644
--- a/crates/viewer/src/main.rs
+++ b/crates/viewer/src/main.rs
@@ -262,7 +262,8 @@ impl GameApp for ViewerApp {
                 self.camera.pan(TOUCHPAD_PAN_MULTIPLIER * camera_space_delta);
             },
             WindowEvent::TouchpadMagnify { delta, .. } => {
-                self.camera.zoom(*delta as f32 * TOUCHPAD_ZOOM_MULTIPLIER);
+                let zoom_delta = *delta as f32 * TOUCHPAD_ZOOM_MULTIPLIER;
+                self.camera.zoom(-zoom_delta);
             },
             WindowEvent::KeyboardInput {
                 input: KeyboardInput { virtual_keycode: Some(keycode), .. },