diff --git a/public/tier0/memalloc.h b/public/tier0/memalloc.h
index b311684c..e64f6688 100644
--- a/public/tier0/memalloc.h
+++ b/public/tier0/memalloc.h
@@ -14,7 +14,7 @@
 #pragma once
 #endif
 
-#if !defined(NO_MALLOC_OVERRIDE) && defined(_POSIX)
+#if !defined(NO_MALLOC_OVERRIDE) && defined(POSIX)
 #define NO_MALLOC_OVERRIDE
 #endif
 
diff --git a/public/tier0/memdbgon.h b/public/tier0/memdbgon.h
index 308b0b8b..ef9a2cfb 100644
--- a/public/tier0/memdbgon.h
+++ b/public/tier0/memdbgon.h
@@ -11,7 +11,7 @@
 // to include this potentially multiple times (since we can deactivate debugging
 // by including memdbgoff.h)
 
-#if !defined(NO_MALLOC_OVERRIDE) && defined(_POSIX)
+#if !defined(NO_MALLOC_OVERRIDE) && defined(POSIX)
 #define NO_MALLOC_OVERRIDE
 #endif