diff --git a/.github/workflows/build-publish.yml b/.github/workflows/build-publish.yml
index 7398f1b..6bdffae 100644
--- a/.github/workflows/build-publish.yml
+++ b/.github/workflows/build-publish.yml
@@ -14,7 +14,7 @@ on:
       xcode_version:
         description: 'The Xcode version to use for building'
         required: true
-        default: '26.3.0'
+        default: '26.5.0'
         type: string
       macos_version:
         description: 'The minimum macOS version to support'
@@ -49,7 +49,7 @@ permissions:
 
 jobs:
   build-macos-arm64:
-    runs-on: macos-latest
+    runs-on: macos-26
     env:
       TARGET_PLATFORM: macos-arm64
     steps:
diff --git a/.github/workflows/dry-run.yml b/.github/workflows/dry-run.yml
index 1889629..09c9f37 100644
--- a/.github/workflows/dry-run.yml
+++ b/.github/workflows/dry-run.yml
@@ -9,15 +9,15 @@ permissions:
   contents: read
 
 env:
-  SWIFT_SYNTAX_VERSION: 602.0.0
-  XCODE_VERSION: 26.3.0
-  RULES_SWIFT_VERSION: 3.1.2
+  SWIFT_SYNTAX_VERSION: 603.0.1
+  XCODE_VERSION: 26.5.0
+  RULES_SWIFT_VERSION: 3.6.1
   MACOS_VERSION: 13.0
   SWIFT_VERSION_LINUX: "6.2"
 
 jobs:
   build-macos-arm64:
-    runs-on: macos-latest
+    runs-on: macos-26
     env:
       TARGET_PLATFORM: macos-arm64
     steps:
diff --git a/build.sh b/build.sh
index eacf1b7..c00fc68 100755
--- a/build.sh
+++ b/build.sh
@@ -15,7 +15,7 @@ set -euo pipefail
 #
 # Build phase expects apple/swift-syntax checked out at ./swift-syntax.
 
-APPLE_SUPPORT_VERSION="${APPLE_SUPPORT_VERSION:-1.23.1}"
+APPLE_SUPPORT_VERSION="${APPLE_SUPPORT_VERSION:-2.5.4}"
 RULES_APPLE_VERSION="${RULES_APPLE_VERSION:-4.2.0}"
 MACOS_VERSION="${MACOS_VERSION:-13.0}"
 
@@ -115,6 +115,15 @@ bazel_dep(name = "rules_swift", version = "$RULES_SWIFT_VERSION", repo_name = "b
 bazel_dep(name = "rules_apple", version = "$RULES_APPLE_VERSION", repo_name = "build_bazel_rules_apple")
 EOF
 
+  # swift-syntax's BUILD.bazel through 603.0.1 omits SwiftIfConfig
+  # from SwiftSyntaxMacros' deps even though Package.swift lists it
+  # and the source `public import`s it. Fixed upstream post-603.0.1
+  # in 9acadd6e; patch in place so the prebuilt build doesn't fail
+  # SwiftSyntaxMacros. buildozer exits 3 (no change) if the dep is
+  # already present -- tolerate that under `set -e`.
+  # TODO: remove this after swift-syntax 604.0.0 ships.
+  buildozer "add deps :SwiftIfConfig" //:SwiftSyntaxMacros || [ $? -eq 3 ]
+
   local -a build_flags
   build_flags=(
     "--@build_bazel_rules_swift//swift:copt=-whole-module-optimization"