--- a/memory/build/mozjemalloc.cpp
+++ b/memory/build/mozjemalloc.cpp
@@ -166,17 +166,20 @@ using namespace mozilla;
 // The jemalloc_purge_freed_pages definition in memory/build/mozmemory.h needs
 // to be adjusted if MALLOC_DOUBLE_PURGE is ever enabled on Linux.
 
 #ifdef XP_DARWIN
 #define MALLOC_DOUBLE_PURGE
 #endif
 
 #ifdef XP_WIN
-
+#define MALLOC_DECOMMIT
+#endif
+
+#ifdef XP_WIN
 #define STDERR_FILENO 2
 
 // Implement getenv without using malloc.
 static char mozillaMallocOptionsBuf[64];
 
 #define getenv xgetenv
 static char*
 getenv(const char* name)
@@ -184,18 +187,16 @@ getenv(const char* name)
 
   if (GetEnvironmentVariableA(
         name, mozillaMallocOptionsBuf, sizeof(mozillaMallocOptionsBuf)) > 0) {
     return mozillaMallocOptionsBuf;
   }
 
   return nullptr;
 }
-
-#define MALLOC_DECOMMIT
 #endif
 
 #ifndef XP_WIN
 #ifndef MADV_FREE
 #define MADV_FREE MADV_DONTNEED
 #endif
 #ifndef MAP_NOSYNC
 #define MAP_NOSYNC 0