diff --git a/embassy-stm32/src/time.rs b/embassy-stm32/src/time.rs
index 71fe668a9..532877f70 100644
--- a/embassy-stm32/src/time.rs
+++ b/embassy-stm32/src/time.rs
@@ -5,7 +5,6 @@ use core::ops::{Div, Mul};
 
 /// Hertz
 #[derive(Eq, PartialEq, Ord, PartialOrd, Clone, Copy, Debug)]
-#[cfg_attr(feature = "defmt", derive(defmt::Format))]
 pub struct Hertz(pub u32);
 
 impl Display for Hertz {
@@ -14,6 +13,13 @@ impl Display for Hertz {
     }
 }
 
+#[cfg(feature = "defmt")]
+impl defmt::Format for Hertz {
+    fn format(&self, f: defmt::Formatter) {
+        defmt::write!(f, "{=u32} Hz", self.0)
+    }
+}
+
 impl Hertz {
     /// Create a `Hertz` from the given hertz.
     pub const fn hz(hertz: u32) -> Self {