diff --git a/caps/src/Makefile.in b/caps/src/Makefile.in
index 2324780effb..010e21000ad 100644
--- a/caps/src/Makefile.in
+++ b/caps/src/Makefile.in
@@ -60,6 +60,10 @@ CPPSRCS		= \
 		nsSecurityManagerFactory.cpp \
 		$(NULL)
 
+ifdef XPC_IDISPATCH_SUPPORT
+DEFINES += -DXPC_IDISPATCH_SUPPORT
+endif
+
 EXTRA_DSO_LDOPTS = \
 		$(LIBS_DIR) \
 		$(ZLIB_LIBS) \