diff --git a/shell/common/BUILD.gn b/shell/common/BUILD.gn
index f377d643ff1c5..69ab3d5f45b1c 100644
--- a/shell/common/BUILD.gn
+++ b/shell/common/BUILD.gn
@@ -214,6 +214,11 @@ if (enable_unittests) {
       "//third_party/skia",
     ]
 
+    defines = [
+      # Required for MSVC STL
+      "_ENABLE_ATOMIC_ALIGNMENT_FIX"
+    ]
+
     public_configs = []
 
     # SwiftShader only supports x86/x64_64
diff --git a/shell/common/shell_test_external_view_embedder.h b/shell/common/shell_test_external_view_embedder.h
index 4b4a759c00801..72c101ed1f4bc 100644
--- a/shell/common/shell_test_external_view_embedder.h
+++ b/shell/common/shell_test_external_view_embedder.h
@@ -8,11 +8,6 @@
 #include "flutter/flow/embedded_views.h"
 #include "flutter/fml/raster_thread_merger.h"
 
-// Required for MSVC STL
-#ifndef _ENABLE_ATOMIC_ALIGNMENT_FIX
-#define _ENABLE_ATOMIC_ALIGNMENT_FIX
-#endif
-
 namespace flutter {
 
 //------------------------------------------------------------------------------