diff --git a/doc/em/proto.make b/doc/em/proto.make
index 35aecca2d..0df81d452 100644
--- a/doc/em/proto.make
+++ b/doc/em/proto.make
@@ -5,6 +5,7 @@
 TBL=tbl
 
 TARGET_DIR = $(TARGET_HOME)/doc
+SRC_DIR = $(SRC_HOME)/doc/em
 
 head:   $(TARGET_DIR)/em.doc