diff --git a/CHANGELOG.md b/CHANGELOG.md
index 082de926..f0d66867 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -49,6 +49,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Changed
 
+- Use manual impls for blocking spi instead of `Default`.
 - Split `Stream` trait on `Stream` and `StreamISR`.
   Use const generics for `Stream` and `Channel`.
 - [breaking-change] `Timer::new` now just initializes peripheral.
diff --git a/src/spi.rs b/src/spi.rs
index 481a69af..c51b257a 100644
--- a/src/spi.rs
+++ b/src/spi.rs
@@ -587,12 +587,56 @@ where
     }
 }
 
-impl<SPI, PINS> embedded_hal::blocking::spi::transfer::Default<u8> for Spi<SPI, PINS> where
-    SPI: Instance
+impl<SPI, PINS> embedded_hal::blocking::spi::Transfer<u8> for Spi<SPI, PINS>
+where
+    SPI: Instance,
+{
+    type Error = Error;
+
+    fn transfer<'w>(&mut self, words: &'w mut [u8]) -> Result<&'w [u8], Self::Error> {
+        use spi::FullDuplex;
+        for word in words.iter_mut() {
+            nb::block!(self.send(*word))?;
+            *word = nb::block!(self.read())?;
+        }
+
+        Ok(words)
+    }
+}
+
+impl<SPI, PINS> embedded_hal::blocking::spi::Write<u8> for Spi<SPI, PINS>
+where
+    SPI: Instance,
 {
+    type Error = Error;
+
+    fn write(&mut self, words: &[u8]) -> Result<(), Self::Error> {
+        use spi::FullDuplex;
+        for word in words {
+            nb::block!(self.send(*word))?;
+            nb::block!(self.read())?;
+        }
+
+        Ok(())
+    }
 }
 
-impl<SPI, PINS> embedded_hal::blocking::spi::write::Default<u8> for Spi<SPI, PINS> where
-    SPI: Instance
+impl<SPI, PINS> embedded_hal::blocking::spi::WriteIter<u8> for Spi<SPI, PINS>
+where
+    SPI: Instance,
 {
+    type Error = Error;
+
+    fn write_iter<WI>(&mut self, words: WI) -> Result<(), Self::Error>
+    where
+        WI: IntoIterator<Item = u8>,
+    {
+        use spi::FullDuplex;
+        for word in words.into_iter() {
+            nb::block!(self.send(word))?;
+            nb::block!(self.read())?;
+        }
+
+        Ok(())
+    }
 }