From 64cf0a6aa421021b19b2d176a810fd675e225dcc Mon Sep 17 00:00:00 2001
From: Robin Malfait <malfait.robin@gmail.com>
Date: Fri, 9 May 2025 18:12:57 +0200
Subject: [PATCH 1/3] add failing test

---
 crates/oxide/src/extractor/named_utility_machine.rs | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/crates/oxide/src/extractor/named_utility_machine.rs b/crates/oxide/src/extractor/named_utility_machine.rs
index e92baac2ae2c..4b6f1053324f 100644
--- a/crates/oxide/src/extractor/named_utility_machine.rs
+++ b/crates/oxide/src/extractor/named_utility_machine.rs
@@ -415,6 +415,9 @@ mod tests {
             // With numbers
             ("px-5", vec!["px-5"]),
             ("px-2.5", vec!["px-2.5"]),
+            // Underscores followed by numbers
+            ("header_1", vec!["header_1"]),
+            ("header_1_2", vec!["header_1_2"]),
             // With number followed by dash or underscore
             ("text-title1-strong", vec!["text-title1-strong"]),
             ("text-title1_strong", vec!["text-title1_strong"]),

From 179dbdc083fcc51de87a35a3ee2166ee929cb8fa Mon Sep 17 00:00:00 2001
From: Robin Malfait <malfait.robin@gmail.com>
Date: Fri, 9 May 2025 18:13:03 +0200
Subject: [PATCH 2/3] allow `_` before a number

---
 crates/oxide/src/extractor/named_utility_machine.rs | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/crates/oxide/src/extractor/named_utility_machine.rs b/crates/oxide/src/extractor/named_utility_machine.rs
index 4b6f1053324f..7c847a2e2915 100644
--- a/crates/oxide/src/extractor/named_utility_machine.rs
+++ b/crates/oxide/src/extractor/named_utility_machine.rs
@@ -279,7 +279,11 @@ impl Machine for NamedUtilityMachine<ParsingState> {
                 Class::Number => {
                     if !matches!(
                         cursor.prev.into(),
-                        Class::Dash | Class::Dot | Class::Number | Class::AlphaLower
+                        Class::Dash
+                            | Class::Underscore
+                            | Class::Dot
+                            | Class::Number
+                            | Class::AlphaLower
                     ) {
                         return self.restart();
                     }

From 57aa137b9bab422a93ed6ba73166617fe315fb8f Mon Sep 17 00:00:00 2001
From: Robin Malfait <malfait.robin@gmail.com>
Date: Fri, 9 May 2025 18:25:43 +0200
Subject: [PATCH 3/3] update changelog

---
 CHANGELOG.md | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 68a1143d06df..4d76daf0fb56 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,7 +7,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
-- Nothing yet!
+### Fixed
+
+- Allow `_` before numbers during candidate extraction ([#17961](https://github.com/tailwindlabs/tailwindcss/pull/17961))
 
 ## [4.1.6] - 2025-05-09