diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 75c2faa7..1000828f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -140,7 +140,9 @@ jobs:
           yarn turbo run build:android --cache-dir="${{ env.TURBO_CACHE_DIR }}"
 
   build-ios:
-    runs-on: macos-latest
+    # Pinned: macos-latest is mid-migration to macOS 26, whose simulator set
+    # has no iPhone 16 Pro on an iOS >=26 runtime, breaking the harness boot.
+    runs-on: macos-15
     env:
       XCODE_VERSION: 26.3
       TURBO_CACHE_DIR: .turbo/ios
@@ -208,7 +210,9 @@ jobs:
           yarn turbo run build:ios --cache-dir="${{ env.TURBO_CACHE_DIR }}"
 
   test-harness-ios:
-    runs-on: macos-latest
+    # Pinned to macos-15 — see build-ios. macos-26 runners lack a matching
+    # iPhone 16 Pro / iOS >=26 simulator, so the boot step fails intermittently.
+    runs-on: macos-15
     timeout-minutes: 60
     env:
       XCODE_VERSION: 26.3