diff --git a/app/auth.go b/app/auth.go
index 75a84ef..a2db4d9 100644
--- a/app/auth.go
+++ b/app/auth.go
@@ -14,7 +14,7 @@ import (
 
 type RegisterForm struct {
 	Name     string `form:"name"     validate:"required,max=40"`
-	Handle   string `form:"handle"   validate:"required,min=3,max=20"`
+	Handle   string `form:"handle"   validate:"required,min=3,max=30"`
 	Email    string `form:"email"    validate:"required,email"`
 	Password string `form:"password" validate:"required,min=8"`
 }
@@ -51,9 +51,17 @@ func (a *App) login(w http.ResponseWriter, r *http.Request) {
 func (a *App) register(w http.ResponseWriter, r *http.Request) {
 	switch r.Method {
 	case "GET":
-		templating.Render(w, r, "base", "register")
+		templating.Render(w, r, "base", "register", map[string]any{
+			"HandleRegex": lib.HandleRegex.String(),
+		})
 	case "POST":
 		form, _ := md.GetForm[RegisterForm](r)
+
+		if !lib.HandleRegex.Match([]byte(form.Handle)) {
+			http.Redirect(w, r, "?err=ErrInvalidHandle", http.StatusSeeOther)
+			return
+		}
+
 		password, err := lib.GenerateHash(form.Password)
 		if err != nil {
 			http.Error(w, "Something went wrong while generating your password's hash. Please try again!", 500)
diff --git a/lib/messages.go b/lib/messages.go
index f7eec38..2715f5b 100644
--- a/lib/messages.go
+++ b/lib/messages.go
@@ -18,11 +18,13 @@ var Errors = map[string]error{
 	"InvalidCredentials":   errors.New("Invalid credentials."),
 	"AlreadyAuthenticated": errors.New("Already authenticated."),
 	"RequireAuth":          errors.New("You must be logged in to access this content."),
-	"UserNotFound":         errors.New("User not found"),
 	"InvalidSession":       errors.New("Session expired or invalid"),
 
 	"WarnOffline": errors.New("It looks like the server is offline. Some features might not work properly."), // TODO: maybe warnings?
 
+	"UserNotFound":      errors.New("User not found"),
+	"UserInvalidHandle": errors.New("That handle is invalid"),
+
 	"GitInvalidBranchName": errors.New("Invalid branch name."),
 	"GitBranchTooLong":     errors.New("Branch too long!"),
 	"GitBranchTooShort":    errors.New("Branch too short!"),
diff --git a/views/register.html b/views/register.html
index 55b51a0..d900489 100644
--- a/views/register.html
+++ b/views/register.html
@@ -6,8 +6,14 @@
     <label for="handle">Handle.</label>
     <div class="handle-container">
         <span>~</span>
-        <input type="text" name="handle" id="handle" autocomplete="off" required>
+        <input type="text" name="handle" id="handle" autocomplete="off" required pattern="{{.HandleRegex}}">
     </div>
+    <details>
+        <summary>View handle regex/rules.</summary>
+        <code>{{.HandleRegex}}</code><br>
+        <span><em>TL;DR:</em> Doesn't start with a dash, has alphanumeric characters, doesn't contain two consecutive
+            dashes, and is between 3 and 30 characters.</span>
+    </details>
     <label for="email">Email.</label>
     <input type="email" name="email" id="email" autocomplete="email" required>
     <label for="password">Password.</label>
@@ -15,7 +21,8 @@
     <button type="submit">Submit.</button>
 </form>
 <style>
-    input:not(.handle-container input), button[type="submit"] {
+    input:not(.handle-container input),
+    button[type="submit"] {
         width: 100%;
     }
 
@@ -23,6 +30,7 @@
         display: flex;
         border: 1px solid var(--link-col);
         padding: 0;
+        width: 100%;
 
         input {
             flex: 1;