diff --git a/src/appdb.js b/src/appdb.js
index 1ed7f5ac6..c16f8e25c 100644
--- a/src/appdb.js
+++ b/src/appdb.js
@@ -475,7 +475,7 @@ function setHealth(appId, health, healthTime, callback) {
 
     var values = { health, healthTime };
 
-    var constraints = 'AND runState NOT LIKE "pending_%" AND installationState = "installed"';
+    var constraints = `AND runState NOT LIKE "pending_%" AND installationState = "${exports.ISTATE_INSTALLED}"`;
 
     updateWithConstraints(appId, values, constraints, callback);
 }
@@ -483,36 +483,13 @@ function setHealth(appId, health, healthTime, callback) {
 function setInstallationCommand(appId, installationState, values, callback) {
     assert.strictEqual(typeof appId, 'string');
     assert.strictEqual(typeof installationState, 'string');
-
-    if (typeof values === 'function') {
-        callback = values;
-        values = { };
-    } else {
-        assert.strictEqual(typeof values, 'object');
-        assert.strictEqual(typeof callback, 'function');
-    }
+    assert.strictEqual(typeof values, 'object');
+    assert.strictEqual(typeof callback, 'function');
 
     values.installationState = installationState;
     values.errorMessage = '';
 
-    // Rules are:
-    // uninstall is allowed in any state
-    // force update is allowed in any state including pending_uninstall! (for better or worse)
-    // restore is allowed from installed or error state or currently restoring
-    // configure is allowed in installed state or currently configuring or in error state
-    // update and backup are allowed only in installed state
-
-    if (installationState === exports.ISTATE_PENDING_UNINSTALL || installationState === exports.ISTATE_PENDING_FORCE_UPDATE) {
-        updateWithConstraints(appId, values, '', callback);
-    } else if (installationState === exports.ISTATE_PENDING_RESTORE) {
-        updateWithConstraints(appId, values, 'AND (installationState = "installed" OR installationState = "error" OR installationState = "pending_restore")', callback);
-    } else if (installationState === exports.ISTATE_PENDING_UPDATE || installationState === exports.ISTATE_PENDING_BACKUP) {
-        updateWithConstraints(appId, values, 'AND installationState = "installed"', callback);
-    } else if (installationState === exports.ISTATE_PENDING_CONFIGURE) {
-        updateWithConstraints(appId, values, 'AND (installationState = "installed" OR installationState = "pending_configure" OR installationState = "error")', callback);
-    } else {
-        callback(new DatabaseError(DatabaseError.INTERNAL_ERROR, 'invalid installationState'));
-    }
+    updateWithConstraints(appId, values, `AND (installationState = "${exports.ISTATE_INSTALLED}" OR installationState = "${exports.ISTATE_ERROR}")`, callback);
 }
 
 function setRunCommand(appId, runState, callback) {
@@ -521,7 +498,7 @@ function setRunCommand(appId, runState, callback) {
     assert.strictEqual(typeof callback, 'function');
 
     var values = { runState: runState };
-    updateWithConstraints(appId, values, 'AND runState NOT LIKE "pending_%" AND installationState = "installed"', callback);
+    updateWithConstraints(appId, values, `AND installationState = "${exports.ISTATE_INSTALLED}"`, callback);
 }
 
 function getAppStoreIds(callback) {
diff --git a/src/apps.js b/src/apps.js
index d734809af..b38460ba5 100644
--- a/src/apps.js
+++ b/src/apps.js
@@ -750,6 +750,7 @@ function configure(appId, data, user, auditSource, callback) {
 
     get(appId, function (error, app) {
         if (error) return callback(error);
+        if (app.installationState !== appdb.ISTATE_INSTALLED && app.installationState !== appdb.ISTATE_ERROR) return callback(new AppsError(AppsError.BAD_STATE, `Not allowed in this app state : ${app.installationState}`));
 
         let domain, location, portBindings, values = { };
         if ('location' in data && 'domain' in data) {
@@ -896,6 +897,7 @@ function update(appId, data, auditSource, callback) {
 
     get(appId, function (error, app) {
         if (error) return callback(error);
+        if (app.installationState !== appdb.ISTATE_INSTALLED && app.installationState !== appdb.ISTATE_ERROR) return callback(new AppsError(AppsError.BAD_STATE, `Not allowed in this app state : ${app.installationState}`));
 
         downloadManifest(data.appStoreId, data.manifest, function (error, appStoreId, manifest) {
             if (error) return callback(error);
@@ -1029,6 +1031,7 @@ function restore(appId, data, auditSource, callback) {
 
     get(appId, function (error, app) {
         if (error) return callback(error);
+        if (app.installationState !== appdb.ISTATE_INSTALLED && app.installationState !== appdb.ISTATE_ERROR) return callback(new AppsError(AppsError.BAD_STATE, `Not allowed in this app state : ${app.installationState}`));
 
         // for empty or null backupId, use existing manifest to mimic a reinstall
         var func = data.backupId ? backups.get.bind(null, data.backupId) : function (next) { return next(null, { manifest: app.manifest }); };
@@ -1186,6 +1189,7 @@ function uninstall(appId, auditSource, callback) {
 
     get(appId, function (error, app) {
         if (error) return callback(error);
+        if (app.installationState !== appdb.ISTATE_INSTALLED && app.installationState !== appdb.ISTATE_ERROR) return callback(new AppsError(AppsError.BAD_STATE, `Not allowed in this app state : ${app.installationState}`));
 
         appstore.unpurchaseApp(appId, { appstoreId: app.appStoreId, manifestId: app.manifest.id }, function (error) {
             if (error && error.reason === AppstoreError.NOT_FOUND) return callback(new AppsError(AppsError.NOT_FOUND));
@@ -1216,11 +1220,17 @@ function start(appId, callback) {
 
     debug('Will start app with id:%s', appId);
 
-    appdb.setRunCommand(appId, appdb.RSTATE_PENDING_START, function (error) {
-        if (error && error.reason === DatabaseError.NOT_FOUND) return callback(new AppsError(AppsError.BAD_STATE)); // might be a bad guess
-        if (error) return callback(new AppsError(AppsError.INTERNAL_ERROR, error));
+    get(appId, function (error, app) {
+        if (error) return callback(error);
+        if (app.installationState !== appdb.ISTATE_INSTALLED) return callback(new AppsError(AppsError.BAD_STATE, `Not allowed in this app state : ${app.installationState}`));
+        if (app.runState !== appdb.RSTATE_STOPPED) return callback(new AppsError(AppsError.BAD_STATE, `Not allowed in this app state : ${app.installationState}`));
 
-        scheduleTask(appId, {}, callback);
+        appdb.setRunCommand(appId, appdb.RSTATE_PENDING_START, function (error) {
+            if (error && error.reason === DatabaseError.NOT_FOUND) return callback(new AppsError(AppsError.BAD_STATE)); // might be a bad guess
+            if (error) return callback(new AppsError(AppsError.INTERNAL_ERROR, error));
+
+            scheduleTask(appId, {}, callback);
+        });
     });
 }
 
@@ -1230,11 +1240,17 @@ function stop(appId, callback) {
 
     debug('Will stop app with id:%s', appId);
 
-    appdb.setRunCommand(appId, appdb.RSTATE_PENDING_STOP, function (error) {
-        if (error && error.reason === DatabaseError.NOT_FOUND) return callback(new AppsError(AppsError.BAD_STATE)); // might be a bad guess
-        if (error) return callback(new AppsError(AppsError.INTERNAL_ERROR, error));
+    get(appId, function (error, app) {
+        if (error) return callback(error);
+        if (app.installationState !== appdb.ISTATE_INSTALLED) return callback(new AppsError(AppsError.BAD_STATE, `Not allowed in this app state : ${app.installationState}`));
+        if (app.runState !== appdb.RSTATE_RUNNING) return callback(new AppsError(AppsError.BAD_STATE, `Not allowed in this app state : ${app.installationState}`));
 
-        scheduleTask(appId, {}, callback);
+        appdb.setRunCommand(appId, appdb.RSTATE_PENDING_STOP, function (error) {
+            if (error && error.reason === DatabaseError.NOT_FOUND) return callback(new AppsError(AppsError.BAD_STATE)); // might be a bad guess
+            if (error) return callback(new AppsError(AppsError.INTERNAL_ERROR, error));
+
+            scheduleTask(appId, {}, callback);
+        });
     });
 }
 
diff --git a/src/routes/apps.js b/src/routes/apps.js
index 2b34a8929..6ad9028b4 100644
--- a/src/routes/apps.js
+++ b/src/routes/apps.js
@@ -276,6 +276,7 @@ function uninstallApp(req, res, next) {
 
     apps.uninstall(req.params.id, auditSource.fromRequest(req), function (error, result) {
         if (error && error.reason === AppsError.EXTERNAL_ERROR) return next(new HttpError(424, error));
+        if (error && error.reason === AppsError.BAD_STATE) return next(new HttpError(409, error.message));
         if (error && error.reason === AppsError.NOT_FOUND) return next(new HttpError(404, 'No such app'));
         if (error) return next(new HttpError(500, error));
 
diff --git a/src/routes/test/apps-test.js b/src/routes/test/apps-test.js
index 087b485a9..3ce38b8fb 100644
--- a/src/routes/test/apps-test.js
+++ b/src/routes/test/apps-test.js
@@ -228,6 +228,8 @@ function stopBox(done) {
 }
 
 describe('App API', function () {
+    let taskId = '';
+
     before(startBox);
     after(stopBox);
 
@@ -424,6 +426,7 @@ describe('App API', function () {
                     APP_ID = res.body.id;
                     expect(fake2.isDone()).to.be.ok();
                     expect(fake3.isDone()).to.be.ok();
+                    taskId = res.body.taskId;
                     done();
                 });
         });
@@ -500,6 +503,15 @@ describe('App API', function () {
             });
     });
 
+    it('can stop the task', function (done) {
+        superagent.post(SERVER_URL + '/api/v1/tasks/' + taskId + '/stop')
+            .query({ access_token: token })
+            .end(function (err, res) {
+                expect(res.statusCode).to.equal(204);
+                setTimeout(done, 4000); // wait for it to really die
+            });
+    });
+
     it('can uninstall app', function (done) {
         var fake1 = nock(settings.apiServerOrigin()).get(function (uri) { return uri.indexOf('/api/v1/cloudronapps/') >= 0; }).reply(200, { });
         var fake2 = nock(settings.apiServerOrigin()).delete(function (uri) { return uri.indexOf('/api/v1/cloudronapps/') >= 0; }).reply(204, { });