diff --git a/public/tier1/utlmemory.h b/public/tier1/utlmemory.h
index 72264a02..640cc00f 100644
--- a/public/tier1/utlmemory.h
+++ b/public/tier1/utlmemory.h
@@ -21,6 +21,8 @@
 #include "tier0/memalloc.h"
 #include "tier0/memdbgon.h"
 
+#include "mathlib/mathlib.h"
+
 #ifdef _MSC_VER
 #pragma warning (disable:4100)
 #pragma warning (disable:4514)