diff --git a/include/mimalloc/atomic.h b/include/mimalloc/atomic.h
index f4bde7f4..807c4da8 100644
--- a/include/mimalloc/atomic.h
+++ b/include/mimalloc/atomic.h
@@ -133,7 +133,9 @@ static inline void mi_atomic_maxi64_relaxed(volatile int64_t* p, int64_t x) {
 #elif defined(_MSC_VER)
 
 // MSVC C compilation wrapper that uses Interlocked operations to model C11 atomics.
+#ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN
+#endif
 #include <windows.h>
 #include <intrin.h>
 #ifdef _WIN64
@@ -327,7 +329,9 @@ static inline void mi_atomic_yield(void) {
   std::this_thread::yield();
 }
 #elif defined(_WIN32)
+#ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN
+#endif
 #include <windows.h>
 static inline void mi_atomic_yield(void) {
   YieldProcessor();
diff --git a/include/mimalloc/prim.h b/include/mimalloc/prim.h
index ebb31df2..f8a40323 100644
--- a/include/mimalloc/prim.h
+++ b/include/mimalloc/prim.h
@@ -222,7 +222,9 @@ static inline mi_threadid_t _mi_prim_thread_id(void) mi_attr_noexcept;
 // Get a unique id for the current thread.
 #if defined(_WIN32)
 
+#ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN
+#endif
 #include <windows.h>
 static inline mi_threadid_t _mi_prim_thread_id(void) mi_attr_noexcept {
   // Windows: works on Intel and ARM in both 32- and 64-bit
diff --git a/include/mimalloc/track.h b/include/mimalloc/track.h
index 9545f750..a659d940 100644
--- a/include/mimalloc/track.h
+++ b/include/mimalloc/track.h
@@ -82,7 +82,9 @@ defined, undefined, or not accessible at all:
 #define MI_TRACK_HEAP_DESTROY 1
 #define MI_TRACK_TOOL         "ETW"
 
+#ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN
+#endif
 #include <windows.h>
 #include "../src/prim/windows/etw.h"