diff --git a/bundle/config/mutator/populate_current_user.go b/bundle/config/mutator/populate_current_user.go
index bba0457c..b604d671 100644
--- a/bundle/config/mutator/populate_current_user.go
+++ b/bundle/config/mutator/populate_current_user.go
@@ -38,15 +38,17 @@ func (m *populateCurrentUser) Apply(ctx context.Context, b *bundle.Bundle) error
 	return nil
 }
 
+func replaceNonAlphanumeric(r rune) rune {
+	if unicode.IsLetter(r) || unicode.IsDigit(r) {
+		return r
+	}
+	return '_'
+}
+
 // Get a short-form username, based on the user's primary email address.
 // We leave the full range of unicode letters in tact, but remove all "special" characters,
 // including dots, which are not supported in e.g. experiment names.
 func getShortUserName(emailAddress string) string {
-	r := []rune(strings.Split(emailAddress, "@")[0])
-	for i := 0; i < len(r); i++ {
-		if !unicode.IsLetter(r[i]) {
-			r[i] = '_'
-		}
-	}
-	return string(r)
+	local, _, _ := strings.Cut(emailAddress, "@")
+	return strings.Map(replaceNonAlphanumeric, local)
 }
diff --git a/bundle/config/mutator/populate_current_user_test.go b/bundle/config/mutator/populate_current_user_test.go
index 79ec52b8..bbb65e07 100644
--- a/bundle/config/mutator/populate_current_user_test.go
+++ b/bundle/config/mutator/populate_current_user_test.go
@@ -1,6 +1,10 @@
 package mutator
 
-import "testing"
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
 
 func TestPopulateCurrentUser(t *testing.T) {
 	// We need to implement workspace client mocking to implement this test.
@@ -13,28 +17,60 @@ func TestGetShortUserName(t *testing.T) {
 		expected string
 	}{
 		{
-			name:     "test alphanumeric characters",
-			email:    "test.user@example.com",
-			expected: "test_user",
+			email:    "test.user.1234@example.com",
+			expected: "test_user_1234",
 		},
 		{
-			name:     "test unicode characters",
 			email:    "tést.üser@example.com",
 			expected: "tést_üser",
 		},
 		{
-			name:     "test special characters",
 			email:    "test$.user@example.com",
 			expected: "test__user",
 		},
+		{
+			email:    `jöhn.dœ@domain.com`, // Using non-ASCII characters.
+			expected: "jöhn_dœ",
+		},
+		{
+			email:    `first+tag@email.com`, // The plus (+) sign is used for "sub-addressing" in some email services.
+			expected: "first_tag",
+		},
+		{
+			email:    `email@sub.domain.com`, // Using a sub-domain.
+			expected: "email",
+		},
+		{
+			email:    `"_quoted"@domain.com`, // Quoted strings can be part of the local-part.
+			expected: "__quoted_",
+		},
+		{
+			email:    `name-o'mally@website.org`, // Single quote in the local-part.
+			expected: "name_o_mally",
+		},
+		{
+			email:    `user%domain@external.com`, // Percent sign can be used for email routing in legacy systems.
+			expected: "user_domain",
+		},
+		{
+			email:    `long.name.with.dots@domain.net`, // Multiple dots in the local-part.
+			expected: "long_name_with_dots",
+		},
+		{
+			email:    `me&you@together.com`, // Using an ampersand (&) in the local-part.
+			expected: "me_you",
+		},
+		{
+			email:    `user!def!xyz@domain.org`, // The exclamation mark can be valid in some legacy systems.
+			expected: "user_def_xyz",
+		},
+		{
+			email:    `admin@ιντερνετ.com`, // Domain in non-ASCII characters (IDN or Internationalized Domain Name).
+			expected: "admin",
+		},
 	}
 
 	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			result := getShortUserName(tt.email)
-			if result != tt.expected {
-				t.Errorf("getShortUserName(%q) = %q; expected %q", tt.email, result, tt.expected)
-			}
-		})
+		assert.Equal(t, tt.expected, getShortUserName(tt.email))
 	}
 }