diff --git a/src/main/java/org/gelecekbilimde/scienceplatform/auth/model/request/RegisterRequest.java b/src/main/java/org/gelecekbilimde/scienceplatform/auth/model/request/RegisterRequest.java
index 64390c2..f20fbbd 100644
--- a/src/main/java/org/gelecekbilimde/scienceplatform/auth/model/request/RegisterRequest.java
+++ b/src/main/java/org/gelecekbilimde/scienceplatform/auth/model/request/RegisterRequest.java
@@ -31,7 +31,6 @@ public class RegisterRequest {
 
 	@NotBlank
 	@Username
-	@Size(min = 3, max = 20)
 	private String username;
 
 	@NotBlank
diff --git a/src/main/java/org/gelecekbilimde/scienceplatform/common/util/validation/UsernameValidator.java b/src/main/java/org/gelecekbilimde/scienceplatform/common/util/validation/UsernameValidator.java
index 24052fa..dfc76a3 100644
--- a/src/main/java/org/gelecekbilimde/scienceplatform/common/util/validation/UsernameValidator.java
+++ b/src/main/java/org/gelecekbilimde/scienceplatform/common/util/validation/UsernameValidator.java
@@ -6,7 +6,7 @@
 
 class UsernameValidator implements ConstraintValidator<Username, String> {
 
-	private static final String USERNAME_REGEX = "^[a-zA-Z0-9]$";
+	private static final String USERNAME_REGEX = "^[a-zA-Z0-9]{3,20}$";
 
 	@Override
 	public boolean isValid(String value, ConstraintValidatorContext context) {
@@ -23,6 +23,13 @@ public boolean isValid(String value, ConstraintValidatorContext context) {
 			return false;
 		}
 
+		if (value.length() <= 3 || value.length() >= 20) {
+			context.disableDefaultConstraintViolation();
+			context.buildConstraintViolationWithTemplate("Username must be between 3 and 20 characters long")
+				.addConstraintViolation();
+			return false;
+		}
+
 		if (!lowerCasedValue.matches(USERNAME_REGEX)) {
 			context.disableDefaultConstraintViolation();
 			context.buildConstraintViolationWithTemplate("Username must be alphanumeric")