diff --git a/src/cose/serialize.rs b/src/cose/serialize.rs
new file mode 100644
index 00000000..053a30b1
--- /dev/null
+++ b/src/cose/serialize.rs
@@ -0,0 +1,81 @@
+use ciborium::Value;
+use serde::ser::{SerializeMap, SerializeSeq};
+use serde::Serialize;
+use serde_cbor::tags::Tagged;
+
+use crate::cose::mac0;
+
+pub(crate) fn serialize<S: serde::Serializer>(
+    value: Value,
+    tag: Option<u64>,
+    serializer: S,
+) -> mac0::Result<S::Ok, S::Error> {
+    if let Some(tag) = tag {
+        return Tagged::new(Some(tag), value).serialize(serializer);
+    }
+    match value {
+        Value::Bytes(x) => serializer.serialize_bytes(&x),
+        Value::Bool(x) => serializer.serialize_bool(x),
+        Value::Text(x) => serializer.serialize_str(x.as_str()),
+        Value::Null => serializer.serialize_unit(),
+
+        Value::Tag(tag, ref v) => Tagged::new(Some(tag), v).serialize(serializer),
+
+        Value::Float(x) => {
+            let y = x as f32;
+            if (y as f64).to_bits() == x.to_bits() {
+                serializer.serialize_f32(y)
+            } else {
+                serializer.serialize_f64(x)
+            }
+        }
+
+        #[allow(clippy::unnecessary_fallible_conversions)]
+        Value::Integer(x) => {
+            if let Ok(x) = u8::try_from(x) {
+                serializer.serialize_u8(x)
+            } else if let Ok(x) = i8::try_from(x) {
+                serializer.serialize_i8(x)
+            } else if let Ok(x) = u16::try_from(x) {
+                serializer.serialize_u16(x)
+            } else if let Ok(x) = i16::try_from(x) {
+                serializer.serialize_i16(x)
+            } else if let Ok(x) = u32::try_from(x) {
+                serializer.serialize_u32(x)
+            } else if let Ok(x) = i32::try_from(x) {
+                serializer.serialize_i32(x)
+            } else if let Ok(x) = u64::try_from(x) {
+                serializer.serialize_u64(x)
+            } else if let Ok(x) = i64::try_from(x) {
+                serializer.serialize_i64(x)
+            } else if let Ok(x) = u128::try_from(x) {
+                serializer.serialize_u128(x)
+            } else if let Ok(x) = i128::try_from(x) {
+                serializer.serialize_i128(x)
+            } else {
+                unreachable!()
+            }
+        }
+
+        Value::Array(x) => {
+            let mut map = serializer.serialize_seq(Some(x.len()))?;
+
+            for v in x {
+                map.serialize_element(&v)?;
+            }
+
+            map.end()
+        }
+
+        Value::Map(x) => {
+            let mut map = serializer.serialize_map(Some(x.len()))?;
+
+            for (k, v) in x {
+                map.serialize_entry(&k, &v)?;
+            }
+
+            map.end()
+        }
+        _ => unimplemented!(),
+    }
+}