diff --git a/libs/core/input.ts b/libs/core/input.ts
index 05f39e89..20b1dd67 100644
--- a/libs/core/input.ts
+++ b/libs/core/input.ts
@@ -13,6 +13,7 @@ namespace sensors.internal {
 
         control.runInBackground(() => {
             let prev = query()
+            changeHandler(prev, prev)
             while (true) {
                 loops.pause(periodMs)
                 let curr = query()
@@ -183,7 +184,7 @@ namespace sensors.internal {
         Low = 3,
     }
 
-    export class ThresholdDetector {        
+    export class ThresholdDetector {
         public id: number;
         private min: number;
         private max: number;
diff --git a/libs/core/linux.cpp b/libs/core/linux.cpp
index e3f16705..5821d191 100644
--- a/libs/core/linux.cpp
+++ b/libs/core/linux.cpp
@@ -393,6 +393,10 @@ static void runPoller(Thread *thr) {
     // note that this is run without the user mutex held - it should not modify any state!
     TValue prev = pxt::runAction0(query);
 
+    startUser();
+    pxt::runAction2(thr->act, prev, prev);
+    stopUser();
+
     while (true) {
         sleep_core_us(us);
         if (paniced)
diff --git a/libs/ev3/pxt.json b/libs/ev3/pxt.json
index 61752d25..5a3c7634 100644
--- a/libs/ev3/pxt.json
+++ b/libs/ev3/pxt.json
@@ -3,7 +3,8 @@
     "description": "The EV3 library",
     "files": [
         "README.md",
-        "ns.ts"
+        "ns.ts",
+        "startup.ts"
     ],
     "dependencies": {
         "base": "file:../base",
diff --git a/libs/ev3/startup.ts b/libs/ev3/startup.ts
new file mode 100644
index 00000000..3dcce976
--- /dev/null
+++ b/libs/ev3/startup.ts
@@ -0,0 +1,4 @@
+// This is the last thing executed before user code
+
+// We pause for 100ms to give time to read sensor values, so they work in on_start block
+loops.pause(100)