diff --git a/esphome/components/adc/adc_sensor_rp2.cpp b/esphome/components/adc/adc_sensor_rp2.cpp
index 2732f5328b..8652a46029 100644
--- a/esphome/components/adc/adc_sensor_rp2.cpp
+++ b/esphome/components/adc/adc_sensor_rp2.cpp
@@ -19,6 +19,25 @@ namespace esphome::adc {
 
 static const char *const TAG = "adc.rp2";
 
+// The on-die temperature sensor sits on the last ADC channel: input 4 on RP2040
+// and RP2350A, but input 8 on RP2350B, which has eight external channels rather
+// than four.
+//
+// This deliberately does not use the SDK's ADC_TEMPERATURE_CHANNEL_NUM. That
+// derives from NUM_ADC_CHANNELS, which <pico.h> settles from a board header, and
+// arduino-pico supplies a fixed B-die one for every RP2350 build. The real die
+// is only declared later, by the variant's pins_arduino.h, so the SDK constant
+// reads 8 on A-die boards. PICO_RP2350A itself is correct by the time this file
+// is compiled, on both arduino-pico and pico-sdk builds.
+#if defined(PICO_RP2350) && !defined(PICO_RP2350A)
+#error "PICO_RP2350A is not defined, so the RP2350 die is unknown and the temperature ADC channel cannot be chosen"
+#endif
+#if defined(PICO_RP2350) && !PICO_RP2350A
+static constexpr uint8_t TEMPERATURE_ADC_INPUT = 8;
+#else
+static constexpr uint8_t TEMPERATURE_ADC_INPUT = 4;
+#endif
+
 void ADCSensor::setup() {
   static bool initialized = false;
   if (!initialized) {
@@ -52,11 +71,7 @@ float ADCSensor::sample() {
   if (this->is_temperature_) {
     adc_set_temp_sensor_enabled(true);
     delay(1);
-    // The on-die temperature sensor sits on the last ADC channel, and which one
-    // that is depends on the chip: input 4 on RP2040 and RP2350A, but input 8 on
-    // RP2350B, which has eight external channels instead of four. The SDK
-    // resolves it for the target being built, so do not hardcode it.
-    adc_select_input(ADC_TEMPERATURE_CHANNEL_NUM);
+    adc_select_input(TEMPERATURE_ADC_INPUT);
 
     for (uint8_t sample = 0; sample < this->sample_count_; sample++) {
       raw = adc_read();