diff --git a/lost/src/main/java/com/mapzen/android/lost/internal/FusedLocationProviderApiImpl.java b/lost/src/main/java/com/mapzen/android/lost/internal/FusedLocationProviderApiImpl.java
index 18a4ea9..e3c4bec 100644
--- a/lost/src/main/java/com/mapzen/android/lost/internal/FusedLocationProviderApiImpl.java
+++ b/lost/src/main/java/com/mapzen/android/lost/internal/FusedLocationProviderApiImpl.java
@@ -8,6 +8,7 @@
 import android.content.Context;
 import android.location.Location;
 import android.os.Looper;
+import android.support.annotation.VisibleForTesting;
 
 import java.io.File;
 import java.util.ArrayList;
@@ -42,9 +43,12 @@ public Location getLastLocation() {
 
     @Override
     public void requestLocationUpdates(LocationRequest request, LocationListener listener) {
+        LocationEngine existing = locationEngines.get(request);
         LocationEngine engine = locationEngineForRequest(request);
         addListenerForEngine(engine, listener);
-        engine.setRequest(request);
+        if (existing == null) {
+            engine.setRequest(request);
+        }
     }
 
     @Override
@@ -80,7 +84,7 @@ public void setMockMode(boolean isMockMode) {
 
     private void toggleMockMode() {
         mockMode = !mockMode;
-        shutdownAllEngines();
+        toggleAllEngines();
         if (mockMode) {
             lastLocationEngine = new MockEngine(context, null);
         } else {
@@ -182,6 +186,41 @@ private LocationEngine removeListenerFromEngine(LocationListener listener) {
         return null;
     }
 
+    private void toggleAllEngines() {
+        HashMap<LocationRequest, LocationEngine> enginesToAdd = new HashMap<>();
+        HashMap<LocationEngine, List<LocationListener>> listenersToAdd = new HashMap<>();
+        for (LocationRequest request : locationEngines.keySet()) {
+            LocationEngine existing = locationEngines.get(request);
+            LocationEngine engineToAdd;
+            if (mockMode) {
+                engineToAdd = new MockEngine(context, this);
+            } else {
+                engineToAdd = new FusionEngine(context, this);
+            }
+            enginesToAdd.put(request, engineToAdd);
+
+            List<LocationListener> listeners = engineListeners.get(existing);
+            listenersToAdd.put(engineToAdd, listeners);
+
+            //Cleanup listeners
+            engineListeners.remove(existing);
+            existing.setRequest(null);
+        }
+        //Cleanup engines
+        locationEngines.clear();
+
+        //Now add new engines/listeners
+        for (LocationRequest request : enginesToAdd.keySet()) {
+            LocationEngine engine = enginesToAdd.get(request);
+            List<LocationListener> listeners = listenersToAdd.get(engine);
+            if (listeners != null) {
+                for (LocationListener listener : listeners) {
+                    requestLocationUpdates(request, listener);
+                }
+            }
+        }
+    }
+
     private void shutdownAllEngines() {
         for (LocationEngine engine : locationEngines.values()) {
             engineListeners.remove(engine);
@@ -189,4 +228,13 @@ private void shutdownAllEngines() {
         }
         locationEngines.clear();
     }
+
+    @VisibleForTesting
+    List<LocationListener> getListeners() {
+        List<LocationListener> listeners = new ArrayList<>();
+        for (LocationEngine engine : engineListeners.keySet()) {
+            listeners.addAll(engineListeners.get(engine));
+        }
+        return listeners;
+    }
 }
diff --git a/lost/src/main/java/com/mapzen/android/lost/internal/LostApiClientImpl.java b/lost/src/main/java/com/mapzen/android/lost/internal/LostApiClientImpl.java
index 0bb3276..93e911f 100644
--- a/lost/src/main/java/com/mapzen/android/lost/internal/LostApiClientImpl.java
+++ b/lost/src/main/java/com/mapzen/android/lost/internal/LostApiClientImpl.java
@@ -41,4 +41,5 @@ public void disconnect() {
     public boolean isConnected() {
         return LocationServices.FusedLocationApi != null && LocationServices.GeofencingApi != null;
     }
+    
 }
diff --git a/lost/src/test/java/com/mapzen/android/lost/internal/FusedLocationProviderApiImplTest.java b/lost/src/test/java/com/mapzen/android/lost/internal/FusedLocationProviderApiImplTest.java
index fc1383f..9ead8e5 100644
--- a/lost/src/test/java/com/mapzen/android/lost/internal/FusedLocationProviderApiImplTest.java
+++ b/lost/src/test/java/com/mapzen/android/lost/internal/FusedLocationProviderApiImplTest.java
@@ -222,6 +222,16 @@ public void setMockMode_shouldNotRegisterDuplicateListeners() throws Exception {
         assertThat(shadowLocationManager.getRequestLocationUpdateListeners()).hasSize(2);
     }
 
+    @Test
+    public void setMockMode_shouldToggleEngines() {
+        TestLocationListener listener = new TestLocationListener();
+        LocationRequest request = LocationRequest.create();
+        api.requestLocationUpdates(request, listener);
+        api.setMockMode(true);
+        api.requestLocationUpdates(request, listener);
+        assertThat(api.getListeners()).hasSize(2);
+    }
+
     @Test
     public void requestLocationUpdates_shouldNotRegisterListenersWithMockModeOn() throws Exception {
         api.setMockMode(true);