diff --git a/mongoose.c b/mongoose.c
index 4dc2ab10..929cd759 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -64,7 +64,9 @@ typedef struct _stati64 file_stat_t;
 #define snprintf _snprintf
 #define vsnprintf _vsnprintf
 #define INT64_FMT  "I64d"
+#ifndef EINPROGRESS
 #define EINPROGRESS WSAEINPROGRESS
+#endif
 #define mutex_init(x) InitializeCriticalSection(x)
 #define mutex_destroy(x) DeleteCriticalSection(x)
 #define mutex_lock(x) EnterCriticalSection(x)