diff --git a/src/VBox/Additions/common/VBoxGuest/linux/Makefile b/src/VBox/Additions/common/VBoxGuest/linux/Makefile
index b403647..cd58fcb 100644
--- a/src/VBox/Additions/common/VBoxGuest/linux/Makefile
+++ b/src/VBox/Additions/common/VBoxGuest/linux/Makefile
@@ -108,7 +108,7 @@ endif
 
 MOD_DEFS = -DVBOX -DRT_OS_LINUX -DIN_RING0 -DIN_RT_R0 -DIN_GUEST \
             -DIN_GUEST_R0 -DIN_MODULE -DRT_WITH_VBOX -DVBGL_VBOXGUEST \
-            -DVBOX_WITH_HGCM
+            -DVBOX_WITH_HGCM -DLOG_USE_C99
 ifeq ($(BUILD_TARGET_ARCH),amd64)
  MOD_DEFS  += -DRT_ARCH_AMD64
 else
