diff --git a/embassy-stm32/src/adc/g4.rs b/embassy-stm32/src/adc/g4.rs
index f6741f019..221cc2a40 100644
--- a/embassy-stm32/src/adc/g4.rs
+++ b/embassy-stm32/src/adc/g4.rs
@@ -170,7 +170,7 @@ impl<'d, T: Instance> Adc<'d, T> {
 
     fn configure_differential_inputs(&mut self) {
         T::regs().difsel().modify(|w| {
-            for n in 0..20 {
+            for n in 0..18 {
                 w.set_difsel(n, Difsel::SINGLEENDED);
             }
         });