diff --git a/Cargo.toml b/Cargo.toml
index 66cd1dd2..6d448013 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,9 +14,7 @@ edition = "2018"
 
 [dependencies]
 diesel = { version = "1.4.3", optional = true }
-once_cell = "1.2.0"
 rand = "0.7.2"
-regex = "1.3.1"
 serde = "1.0.102"
 url = "2.1.0"
 
diff --git a/src/user_id.rs b/src/user_id.rs
index 9bb8fb28..255ae416 100644
--- a/src/user_id.rs
+++ b/src/user_id.rs
@@ -7,8 +7,6 @@ use std::{
 
 #[cfg(feature = "diesel")]
 use diesel::sql_types::Text;
-use once_cell::sync::Lazy;
-use regex::Regex;
 use serde::{
     de::{Error as SerdeError, Unexpected, Visitor},
     Deserialize, Deserializer, Serialize, Serializer,
@@ -17,11 +15,6 @@ use url::Host;
 
 use crate::{display, error::Error, generate_localpart, parse_id};
 
-// See https://matrix.org/docs/spec/appendices#user-identifiers
-static USER_LOCALPART_PATTERN: Lazy<Regex> = Lazy::new(|| {
-    Regex::new(r"\A[a-z0-9\-.=_/]+\z").expect("Failed to create user localpart regex.")
-});
-
 /// A Matrix user ID.
 ///
 /// A `UserId` is generated randomly or converted from a string slice, and can be converted back
@@ -124,7 +117,11 @@ impl<'a> TryFrom<&'a str> for UserId {
         let (localpart, host, port) = parse_id('@', user_id)?;
         let downcased_localpart = localpart.to_lowercase();
 
-        if !USER_LOCALPART_PATTERN.is_match(&downcased_localpart) {
+        // See https://matrix.org/docs/spec/appendices#user-identifiers
+        if downcased_localpart.bytes().any(|b| match b {
+            b'0'..=b'9' | b'a'..=b'z' | b'-' | b'.' | b'=' | b'_' | b'/' => false,
+            _ => true,
+        }) {
             return Err(Error::InvalidCharacters);
         }