diff --git a/glslang/Include/PoolAlloc.h b/glslang/Include/PoolAlloc.h
index 1f5cac76..15adbaf0 100644
--- a/glslang/Include/PoolAlloc.h
+++ b/glslang/Include/PoolAlloc.h
@@ -37,7 +37,7 @@
 #ifndef _POOLALLOC_INCLUDED_
 #define _POOLALLOC_INCLUDED_
 
-#ifdef _DEBUG
+#ifndef NDEBUG
 #  define GUARD_BLOCKS  // define to enable guard block sanity checking
 #endif