-SGML_TEX = $(SGML_DOC).tex
-SGML_DVI = $(SGML_DOC).dvi
-SGML_PS = $(SGML_DOC).ps
-SGML_PDF = $(SGML_DOC).pdf
-SGML_RTF = $(SGML_DOC).rtf
-SGML_HTML = $(SGML_DOC).html
+SGML_TEX = $(addsuffix .tex,$(SGML_DOC))
+SGML_DVI = $(addsuffix .dvi,$(SGML_DOC))
+SGML_PS = $(addsuffix .ps,$(SGML_DOC))
+SGML_PDF = $(addsuffix .pdf,$(SGML_DOC))
+SGML_RTF = $(addsuffix .rtf,$(SGML_DOC))
+SGML_HTML = $(addsuffix .html,$(SGML_DOC))