diff --git a/misc/multiaddr/src/errors.rs b/misc/multiaddr/src/errors.rs
index 2636358319e..964cdffff50 100644
--- a/misc/multiaddr/src/errors.rs
+++ b/misc/multiaddr/src/errors.rs
@@ -14,7 +14,7 @@ pub enum Error {
     InvalidUvar(decode::Error),
     ParsingError(Box<dyn error::Error + Send + Sync>),
     UnknownProtocolId(u32),
-    UnknownProtocolString,
+    UnknownProtocolString(String),
     #[doc(hidden)]
     __Nonexhaustive
 }
@@ -28,7 +28,7 @@ impl fmt::Display for Error {
             Error::InvalidUvar(e) => write!(f, "failed to decode unsigned varint: {}", e),
             Error::ParsingError(e) => write!(f, "failed to parse: {}", e),
             Error::UnknownProtocolId(id) => write!(f, "unknown protocol id: {}", id),
-            Error::UnknownProtocolString => f.write_str("unknown protocol string"),
+            Error::UnknownProtocolString(string) => write!(f, "unknown protocol string: {}", string),
             Error::__Nonexhaustive => f.write_str("__Nonexhaustive")
         }
     }
diff --git a/misc/multiaddr/src/protocol.rs b/misc/multiaddr/src/protocol.rs
index 2b687b126e9..e424a5c746c 100644
--- a/misc/multiaddr/src/protocol.rs
+++ b/misc/multiaddr/src/protocol.rs
@@ -171,7 +171,7 @@ impl<'a> Protocol<'a> {
                 let s = iter.next().ok_or(Error::InvalidProtocolString)?;
                 Ok(Protocol::Memory(s.parse()?))
             }
-            _ => Err(Error::UnknownProtocolString)
+            unknown => Err(Error::UnknownProtocolString(unknown.to_string()))
         }
     }
 
diff --git a/misc/multiaddr/tests/lib.rs b/misc/multiaddr/tests/lib.rs
index 0516a682629..d31e45cd953 100644
--- a/misc/multiaddr/tests/lib.rs
+++ b/misc/multiaddr/tests/lib.rs
@@ -328,3 +328,15 @@ fn replace_ip4_with_ip6() {
     assert_eq!(result.unwrap(), "/ip6/2001:db8::1/tcp/10000".parse::<Multiaddr>().unwrap())
 }
 
+#[test]
+fn unknown_protocol_string() {
+    match "/unknown/1.2.3.4".parse::<Multiaddr>() {
+        Ok(_) => assert!(false, "The UnknownProtocolString error should be caused"),
+        Err(e) => match e {
+            crate::Error::UnknownProtocolString(protocol) => {
+                assert_eq!(protocol, "unknown")
+            },
+            _ => assert!(false, "The UnknownProtocolString error should be caused")
+        }
+    }
+}