diff --git a/DroidFish/jni/jni.cpp b/DroidFish/jni/jni.cpp
index 36a985f..3f7a869 100644
--- a/DroidFish/jni/jni.cpp
+++ b/DroidFish/jni/jni.cpp
@@ -31,6 +31,8 @@ int main(int argc, char* argv[]);
 static int fdFromChild = -1;
 static int fdToChild = -1;
 
+static int childpid = -1;
+
 /*
  * Class:     org_petero_droidfish_engine_NativePipedProcess
  * Method:    startProcess
@@ -39,13 +41,16 @@ static int fdToChild = -1;
 extern "C" JNIEXPORT void JNICALL Java_org_petero_droidfish_engine_NativePipedProcess_startProcess
 		(JNIEnv* env, jobject obj)
 {
+    if (childpid != -1)
+        kill(childpid, SIGKILL);
+
 	int fd1[2];		/* parent -> child */
     int fd2[2];		/* child -> parent */
     if (pipe(fd1) < 0)
     	exit(1);
     if (pipe(fd2) < 0)
     	exit(1);
-    int childpid = fork();
+    childpid = fork();
     if (childpid == -1) {
         exit(1);
     }
diff --git a/DroidFish/src/org/petero/droidfish/engine/DroidComputerPlayer.java b/DroidFish/src/org/petero/droidfish/engine/DroidComputerPlayer.java
index b25efa6..c8d9aca 100644
--- a/DroidFish/src/org/petero/droidfish/engine/DroidComputerPlayer.java
+++ b/DroidFish/src/org/petero/droidfish/engine/DroidComputerPlayer.java
@@ -302,6 +302,7 @@ public class DroidComputerPlayer {
     /** Start an engine, if not already started.
      * Will shut down old engine first, if needed. */
     public final synchronized void queueStartEngine(int id, String engine) {
+        killOldEngine(engine);
         stopSearch();
         searchRequest = SearchRequest.startRequest(id, engine);
         handleQueue();
@@ -314,6 +315,7 @@ public class DroidComputerPlayer {
      * command, such as "draw" and "resign".
      */
     public final synchronized void queueSearchRequest(SearchRequest sr) {
+        killOldEngine(sr.engine);
         stopSearch();
 
         if (sr.ponderMove != null)
@@ -364,6 +366,7 @@ public class DroidComputerPlayer {
 
     /** Start analyzing a position. */
     public final synchronized void queueAnalyzeRequest(SearchRequest sr) {
+        killOldEngine(sr.engine);
         stopSearch();
 
         // If no legal moves, there is nothing to analyze
@@ -385,6 +388,12 @@ public class DroidComputerPlayer {
             handleIdleState();
     }
 
+    private void killOldEngine(String engine) {
+        if (engine.equals(engineState.engine))
+            return;
+        shutdownEngine();
+    }
+
     /** Tell engine to stop searching. */
     public final synchronized boolean stopSearch() {
         searchRequest = null;
@@ -562,7 +571,10 @@ public class DroidComputerPlayer {
     private final void monitorLoop() {
         while (true) {
             int timeout = getReadTimeout();
-            String s = uciEngine.readLineFromEngine(timeout);
+            UCIEngine uci = uciEngine;
+            if (uci == null)
+                return;
+            String s = uci.readLineFromEngine(timeout);
             if (Thread.currentThread().isInterrupted())
                 return;
             processEngineOutput(s);