diff --git a/Sources/_StringProcessing/Engine/MEBuiltins.swift b/Sources/_StringProcessing/Engine/MEBuiltins.swift
index f6d97555d..546721020 100644
--- a/Sources/_StringProcessing/Engine/MEBuiltins.swift
+++ b/Sources/_StringProcessing/Engine/MEBuiltins.swift
@@ -382,7 +382,9 @@ extension String {
       }
     case .word:
       if isScalarSemantics {
-        matched = scalar.properties.isAlphabetic && asciiCheck
+        matched = (scalar.properties.isAlphabetic
+          || scalar.properties.numericType != nil
+          || scalar == "_") && asciiCheck
       } else {
         matched = char.isWordCharacter && asciiCheck
       }
diff --git a/Tests/RegexTests/MatchTests.swift b/Tests/RegexTests/MatchTests.swift
index 2d9a6b1c2..5bf68c106 100644
--- a/Tests/RegexTests/MatchTests.swift
+++ b/Tests/RegexTests/MatchTests.swift
@@ -952,6 +952,17 @@ extension RegexTests {
     firstMatchTest(
       #"(?S)\v"#, input: "\r\n", match: "\r", semanticLevel: .unicodeScalar)
 
+    // \w in scalar semantics must match letters, digits, and underscore
+    // (matching the same definition used in grapheme-cluster semantics),
+    // not just alphabetics.
+    matchTest(
+      #"\w"#,
+      ("a", true),
+      ("1", true),
+      ("_", true),
+      (" ", false),
+      semanticLevel: .unicodeScalar)
+
     matchTest(
       #"[a]\u0301"#,
       ("a\u{301}", false),