diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index e33b7b903..3bf5a95ec 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -11,7 +11,6 @@ jobs:
         name: Unit tests
         uses: apple/swift-nio/.github/workflows/unit_tests.yml@main
         with:
-            linux_5_9_enabled: false
             linux_5_10_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -warnings-as-errors"
             linux_6_0_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -warnings-as-errors"
             linux_6_1_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -warnings-as-errors"
diff --git a/.github/workflows/pull_request.yml b/.github/workflows/pull_request.yml
index 320b3d7de..8036d7ad7 100644
--- a/.github/workflows/pull_request.yml
+++ b/.github/workflows/pull_request.yml
@@ -14,7 +14,6 @@ jobs:
         name: Unit tests
         uses: apple/swift-nio/.github/workflows/unit_tests.yml@main
         with:
-            linux_5_9_enabled: true
             linux_5_10_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -warnings-as-errors"
             linux_6_0_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -warnings-as-errors"
             linux_6_1_arguments_override: "--explicit-target-dependency-import-check error -Xswiftc -warnings-as-errors"
diff --git a/Package.swift b/Package.swift
index 2a58a41a9..3294781a9 100644
--- a/Package.swift
+++ b/Package.swift
@@ -1,4 +1,4 @@
-// swift-tools-version:5.9
+// swift-tools-version:5.10
 //===----------------------------------------------------------------------===//
 //
 // This source file is part of the AsyncHTTPClient open source project
diff --git a/README.md b/README.md
index 02d4aa0b8..a4f49c8c8 100644
--- a/README.md
+++ b/README.md
@@ -306,7 +306,7 @@ Please have a look at [SECURITY.md](SECURITY.md) for AsyncHTTPClient's security
 
 ## Supported Versions
 
-The most recent versions of AsyncHTTPClient support Swift 5.9 and newer. The minimum Swift version supported by AsyncHTTPClient releases are detailed below:
+The most recent versions of AsyncHTTPClient support Swift 5.10 and newer. The minimum Swift version supported by AsyncHTTPClient releases are detailed below:
 
 AsyncHTTPClient     | Minimum Swift Version
 --------------------|----------------------
@@ -317,4 +317,5 @@ AsyncHTTPClient     | Minimum Swift Version
 `1.18.0 ..< 1.20.0` | 5.6
 `1.20.0 ..< 1.21.0` | 5.7
 `1.21.0 ..< 1.26.0` | 5.8
-`1.26.0 ...`        | 5.9
+`1.26.0 ..< 1.27.0` | 5.9
+`1.27.0 ...`        | 5.10
diff --git a/Sources/AsyncHTTPClient/HTTPClient+HTTPCookie.swift b/Sources/AsyncHTTPClient/HTTPClient+HTTPCookie.swift
index 65225752f..759f6728a 100644
--- a/Sources/AsyncHTTPClient/HTTPClient+HTTPCookie.swift
+++ b/Sources/AsyncHTTPClient/HTTPClient+HTTPCookie.swift
@@ -216,21 +216,12 @@ extension String.UTF8View.SubSequence {
     }
 }
 
-#if compiler(>=5.10)
 nonisolated(unsafe) private let posixLocale: UnsafeMutableRawPointer = {
     // All POSIX systems must provide a "POSIX" locale, and its date/time formats are US English.
     // https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap07.html#tag_07_03_05
     let _posixLocale = newlocale(LC_TIME_MASK | LC_NUMERIC_MASK, "POSIX", nil)!
     return UnsafeMutableRawPointer(_posixLocale)
 }()
-#else
-private let posixLocale: UnsafeMutableRawPointer = {
-    // All POSIX systems must provide a "POSIX" locale, and its date/time formats are US English.
-    // https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap07.html#tag_07_03_05
-    let _posixLocale = newlocale(LC_TIME_MASK | LC_NUMERIC_MASK, "POSIX", nil)!
-    return UnsafeMutableRawPointer(_posixLocale)
-}()
-#endif
 
 private func parseTimestamp(_ utf8: String.UTF8View.SubSequence, format: String) -> tm? {
     var timeComponents = tm()