diff --git a/test/user_mgr_test.cpp b/test/user_mgr_test.cpp
index 85a8b0a..94120ff 100644
--- a/test/user_mgr_test.cpp
+++ b/test/user_mgr_test.cpp
@@ -564,9 +564,13 @@
        ThrowForUserNameConstraintsRegexMismatchThrowsInvalidArgument)
 {
     std::string startWithNumber = "0ABC";
+    std::string startWithDisallowedCharacter = "[test";
     EXPECT_THROW(
         throwForUserNameConstraints(startWithNumber, {"ipmi"}),
         sdbusplus::xyz::openbmc_project::Common::Error::InvalidArgument);
+    EXPECT_THROW(
+        throwForUserNameConstraints(startWithDisallowedCharacter, {"ipmi"}),
+        sdbusplus::xyz::openbmc_project::Common::Error::InvalidArgument);
 }
 
 TEST_F(UserMgrInTest, UserAddNotRootFailedWithInternalFailure)
diff --git a/user_mgr.cpp b/user_mgr.cpp
index 4f49925..08cc772 100644
--- a/user_mgr.cpp
+++ b/user_mgr.cpp
@@ -208,7 +208,7 @@
 {
     if (groupName.size() > maxSystemGroupNameLength ||
         !std::regex_match(groupName.c_str(),
-                          std::regex("[a-zA-z_][a-zA-Z_0-9]*")))
+                          std::regex("[a-zA-Z_][a-zA-Z_0-9]*")))
     {
         lg2::error("Invalid group name '{GROUP}'", "GROUP", groupName);
         elog<InvalidArgument>(Argument::ARGUMENT_NAME("Group Name"),
@@ -253,7 +253,7 @@
                               Argument::ARGUMENT_VALUE("Invalid length"));
     }
     if (!std::regex_match(userName.c_str(),
-                          std::regex("[a-zA-z_][a-zA-Z_0-9]*")))
+                          std::regex("[a-zA-Z_][a-zA-Z_0-9]*")))
     {
         lg2::error("Invalid username '{USERNAME}'", "USERNAME", userName);
         elog<InvalidArgument>(Argument::ARGUMENT_NAME("User name"),