diff --git a/mozilla/webshell/tests/viewer/Makefile.in b/mozilla/webshell/tests/viewer/Makefile.in
index 2f3ed4c21f0..b9607b563ce 100644
--- a/mozilla/webshell/tests/viewer/Makefile.in
+++ b/mozilla/webshell/tests/viewer/Makefile.in
@@ -37,7 +37,7 @@ TOOLKIT_CPPSRCS = \
 	nsGTKMain.cpp \
 	nsGTKMenu.cpp
 
-INCLUDES += $(topsrcdir)/widget/src/gtk
+INCLUDES += -I$(topsrcdir)/widget/src/gtk
 
 TOOLKIT_CFLAGS += $(TK_GTK_CFLAGS)
 TOOLKIT_LIBS   = $(TK_GTK_LIBS)