diff --git a/src/PortalTask.h b/src/PortalTask.h
index 23c6635..f50ef23 100644
--- a/src/PortalTask.h
+++ b/src/PortalTask.h
@@ -227,12 +227,8 @@ protected:
       // restore sensors settings
       if (!requestDoc[FPSTR(S_SENSORS)].isNull()) {
         for (auto sensor : requestDoc[FPSTR(S_SENSORS)].as<JsonObject>()) {
-          if (!isDigit(sensor.key().c_str())) {
-            continue;
-          }
-
-          int sensorId = atoi(sensor.key().c_str());
-          if (sensorId < 0 || sensorId > 255 || !Sensors::isValidSensorId(sensorId)) {
+          uint8_t sensorId;
+          if (!Sensors::parseId(sensor.key().c_str(), sensorId)) {
             continue;
           }
 
@@ -420,12 +416,8 @@ protected:
       }
 
       const auto& id = request->getParam("id")->value();
-      if (!isDigit(id.c_str())) {
-        return request->send(400);
-      }
-
-      uint8_t sensorId = id.toInt();
-      if (!Sensors::isValidSensorId(sensorId)) {
+      uint8_t sensorId;
+      if (!Sensors::parseId(id.c_str(), sensorId)) {
         return request->send(404);
       }
 
@@ -451,12 +443,8 @@ protected:
       }
 
       auto& id = request->getParam("id")->value();
-      if (!isDigit(id.c_str())) {
-        return request->send(400);
-      }
-
-      uint8_t sensorId = id.toInt();
-      if (!Sensors::isValidSensorId(sensorId)) {
+      uint8_t sensorId;
+      if (!Sensors::parseId(id.c_str(), sensorId)) {
         return request->send(404);
       }
 
diff --git a/src/Sensors.h b/src/Sensors.h
index fd40a1f..d694a18 100644
--- a/src/Sensors.h
+++ b/src/Sensors.h
@@ -1,4 +1,6 @@
 #pragma once
+#include <errno.h>
+#include <stdlib.h>
 
 class Sensors {
 protected:
@@ -121,10 +123,26 @@ public:
     return maxSensors > 1 ? (maxSensors - 1) : 0;
   }
 
-  static inline bool isValidSensorId(const uint8_t id) {
+  template <class T>
+  static bool isValidSensorId(const T id) {
     return id >= 0 && id <= getMaxSensorId();
   }
 
+  static bool parseId(const char* value, uint8_t& sensorId) {
+    if (!isDigit(value)) {
+      return false;
+    }
+
+    errno = 0;
+    const unsigned long parsed = strtoul(value, nullptr, 10);
+    if (errno == ERANGE || !isValidSensorId(parsed)) {
+      return false;
+    }
+
+    sensorId = static_cast<uint8_t>(parsed);
+    return true;
+  }
+
   static inline bool isValidValueId(const uint8_t id) {
     return id >= (uint8_t) ValueType::TEMPERATURE && id <= (uint8_t) ValueType::RSSI;
   }
@@ -499,6 +517,22 @@ public:
   static uint8_t bluetoothRssiToQuality(int rssi) {
     return constrain(map(rssi, -110, -50, 0, 100), 0, 100);;
   }
+
+private:
+  static constexpr bool isDigit(const char* value) {
+    if (value == nullptr || *value == '\0') {
+      return false;
+    }
+
+    while (*value != '\0') {
+      if (*value < '0' || *value > '9') {
+        return false;
+      }
+      value++;
+    }
+
+    return true;
+  }
 };
 
 uint8_t Sensors::maxSensors = 0;
diff --git a/src/utils.h b/src/utils.h
index 9553bd8..499670b 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -70,12 +70,6 @@ time_t mkgmtime(const struct tm *ptm) {
   return secs;
 }
 
-inline bool isDigit(const char* ptr) {
-  char* endPtr;
-  auto tmp = strtol(ptr, &endPtr, 10);
-  return *endPtr == 0;
-}
-
 inline float liter2gallon(float value) {
   return value / 4.546091879f;
 }