diff --git a/src/machine/machine_stm32_moder_gpio.go b/src/machine/machine_stm32_moder_gpio.go
index c1439eb5..99d913cd 100644
--- a/src/machine/machine_stm32_moder_gpio.go
+++ b/src/machine/machine_stm32_moder_gpio.go
@@ -148,6 +148,7 @@ func (p Pin) ConfigureAltFunc(config PinConfig, altFunc uint8) {
 	// ADC
 	case PinInputAnalog:
 		port.MODER.ReplaceBits(gpioModeAnalog, gpioModeMask, pos)
+		port.PUPDR.ReplaceBits(gpioPullFloating, gpioPullMask, pos)
 	}
 }