diff --git a/core/src/main/scala/weaponregex/internal/parser/Parser.scala b/core/src/main/scala/weaponregex/internal/parser/Parser.scala
index 2f357aa..f46beaf 100644
--- a/core/src/main/scala/weaponregex/internal/parser/Parser.scala
+++ b/core/src/main/scala/weaponregex/internal/parser/Parser.scala
@@ -441,13 +441,13 @@ abstract private[weaponregex] class Parser(val pattern: String) {
   def group[A: P]: P[Group] = Indexed("(" ~ RE ~ ")")
     .map { case (loc, expr) => Group(expr, isCapturing = true, loc) }
 
-  /** Parse a group name that starts with a letter and followed by zero or more alphanumeric characters
+  /** Parse a group name
     * @return
     *   the parsed name string
     * @example
     *   `"name1"`
     */
-  def groupName[A: P]: P[String] = P(CharIn("a-z", "A-Z") ~ CharIn("a-z", "A-Z", "0-9").rep).!
+  def groupName[A: P]: P[String]
 
   /** Parse a named-capturing group
     * @return
diff --git a/core/src/main/scala/weaponregex/internal/parser/ParserJS.scala b/core/src/main/scala/weaponregex/internal/parser/ParserJS.scala
index e34c988..04e4d16 100644
--- a/core/src/main/scala/weaponregex/internal/parser/ParserJS.scala
+++ b/core/src/main/scala/weaponregex/internal/parser/ParserJS.scala
@@ -73,6 +73,15 @@ private[weaponregex] class ParserJS private[parser] (pattern: String, val flags:
     else
       P(preDefinedCharClass | metaCharacter | range | quoteChar | charClassCharLiteral)
 
+  /** Parse a group name
+    * @return
+    *   the parsed name string
+    * @example
+    *   `"name1"`
+    */
+  override def groupName[A: P]: P[String] =
+    P(CharIn("a-z", "A-Z", "_") ~ CharIn("a-z", "A-Z", "0-9", "_").rep).!
+
   /** Parse a quoted character (any character). If [[weaponregex.internal.parser.ParserJS unicodeMode]] is true, only
     * the following characters are allowed: `^ $ \ . * + ? ( ) [ ] { } |` or `/`
     * @return
diff --git a/core/src/main/scala/weaponregex/internal/parser/ParserJVM.scala b/core/src/main/scala/weaponregex/internal/parser/ParserJVM.scala
index ef73368..f986cf3 100644
--- a/core/src/main/scala/weaponregex/internal/parser/ParserJVM.scala
+++ b/core/src/main/scala/weaponregex/internal/parser/ParserJVM.scala
@@ -97,6 +97,15 @@ private[weaponregex] class ParserJVM private[parser] (pattern: String) extends P
     )
       .map { case (loc, (hat, nodes)) => CharacterClass(nodes, loc, isPositive = hat.isEmpty) }
 
+  /** Parse a group name
+    * @return
+    *   the parsed name string
+    * @example
+    *   `"name1"`
+    */
+  override def groupName[A: P]: P[String] =
+    P(CharIn("a-z", "A-Z") ~ CharIn("a-z", "A-Z", "0-9").rep).!
+
   /** Intermediate parsing rule for special construct tokens which can parse either `namedGroup`, `nonCapturingGroup`,
     * `flagToggleGroup`, `flagNCGroup`, `lookaround` or `atomicGroup`
     * @return
diff --git a/core/src/test/scala/weaponregex/internal/parser/ParserJSTest.scala b/core/src/test/scala/weaponregex/internal/parser/ParserJSTest.scala
index e8b5e74..3f208f8 100644
--- a/core/src/test/scala/weaponregex/internal/parser/ParserJSTest.scala
+++ b/core/src/test/scala/weaponregex/internal/parser/ParserJSTest.scala
@@ -293,6 +293,48 @@ class ParserJSTest extends munit.FunSuite with ParserTest {
     treeBuildTest(parsedTree, pattern)
   }
 
+  test("Parse named capturing group with underscores in name") {
+    val pattern = "(?<group_Name_1>hello)(?<Group_Name_2>world)"
+    val parsedTree = Parser(pattern, parserFlavor).getOrFail.to[Concat]
+
+    assert(clue(parsedTree.children.head) match {
+      case NamedGroup(_: Concat, name, _) => name == "group_Name_1"
+      case _                              => false
+    })
+    assert(clue(parsedTree.children.last) match {
+      case NamedGroup(_: Concat, name, _) => name == "Group_Name_2"
+      case _                              => false
+    })
+
+    treeBuildTest(parsedTree, pattern)
+  }
+
+  test("Parse nested named capturing group with underscores in name") {
+    val pattern = "(?<group_Name_1>hello(?<Group_Name_2>world))"
+    val parsedTree = Parser(pattern, parserFlavor).getOrFail
+
+    assert(clue(parsedTree) match {
+      case NamedGroup(Concat(nodes, _), "group_Name_1", _) =>
+        assert(clue(nodes.last) match {
+          case NamedGroup(_: Concat, "Group_Name_2", _) => true
+          case _                                        => false
+        })
+        true
+      case _ => false
+    })
+
+    treeBuildTest(parsedTree, pattern)
+  }
+
+  test("Parse named reference with underscores in name") {
+    val pattern = """\k<name_1>"""
+    val parsedTree = Parser(pattern, parserFlavor).getOrFail.to[NameReference]
+
+    assertEquals(parsedTree.name, "name_1")
+
+    treeBuildTest(parsedTree, pattern)
+  }
+
   test("Unparsable: flag toggle group i-i") {
     val pattern = "(?idmsuxU-idmsuxU)"
     parseErrorTest(pattern)