diff --git a/Sources/_StringProcessing/Engine/Processor.swift b/Sources/_StringProcessing/Engine/Processor.swift
index 049ecaf23..cdd2bd3e5 100644
--- a/Sources/_StringProcessing/Engine/Processor.swift
+++ b/Sources/_StringProcessing/Engine/Processor.swift
@@ -799,7 +799,7 @@ extension String {
     let idx = unicodeScalars.index(after: pos)
     assert(idx <= end, "Input is a substring with a sub-scalar endIndex.")
 
-    if boundaryCheck && !isOnGraphemeClusterBoundary(idx) {
+    if boundaryCheck && idx != end && !isOnGraphemeClusterBoundary(idx) {
       return nil
     }
 
@@ -820,7 +820,7 @@ extension String {
 
     guard cur <= end else { return nil }
 
-    if boundaryCheck && !isOnGraphemeClusterBoundary(cur) {
+    if boundaryCheck && cur != end && !isOnGraphemeClusterBoundary(cur) {
       return nil
     }
 
diff --git a/Tests/RegexTests/MatchTests.swift b/Tests/RegexTests/MatchTests.swift
index b704b1986..f492c345d 100644
--- a/Tests/RegexTests/MatchTests.swift
+++ b/Tests/RegexTests/MatchTests.swift
@@ -3059,6 +3059,18 @@ extension RegexTests {
     XCTAssertNotNil("tesTs".wholeMatch(of: regex))
   }
 
+  func testLiteralAtSubCharacterEnd() throws {
+    let cafe = "cafe\u{301}"
+    let sub = cafe[..<cafe.unicodeScalars.index(before: cafe.endIndex)]
+    for regex in [#/afe/#, #/af./#] {
+      XCTAssertEqual(sub.firstMatch(of: regex)?.0, "afe")
+    }
+    XCTAssertNotNil(sub.firstRange(of: "afe"))
+    
+    // No match for a literal ending sub-character
+    XCTAssertNil(cafe.firstRange(of: Regex<Substring>(verbatim: "afe")))
+  }
+  
   func testAutoPossessificationSkippedNodes() throws {
     firstMatchTest(#"(\w* {0})a"#, input: "a", match: "a")
     firstMatchTest(#"((\w* {0})){1}()a"#, input: "a", match: "a")