diff --git a/intl/icu/source/common/umutex.h b/intl/icu/source/common/umutex.h
--- a/intl/icu/source/common/umutex.h
+++ b/intl/icu/source/common/umutex.h
@@ -315,17 +315,17 @@ U_NAMESPACE_END
 # define NOMCX
 # ifndef NOMINMAX
 # define NOMINMAX
 # endif
 # include <windows.h>
 
 
 typedef struct UMutex {
-    UInitOnce         fInitOnce;
+    icu::UInitOnce    fInitOnce;
     CRITICAL_SECTION  fCS;
 } UMutex;
 
 /* Initializer for a static UMUTEX. Deliberately contains no value for the
  *  CRITICAL_SECTION.
  */
 #define U_MUTEX_INITIALIZER {U_INITONCE_INITIALIZER}