diff --git a/docs/images/Makefile b/docs/images/Makefile
index abb60b3..9a83a34 100644
--- a/docs/images/Makefile
+++ b/docs/images/Makefile
@@ -1,33 +1,33 @@
 
 PY_REQUIREMENTS = $(wildcard ../../../*/requirements*.txt)
 DEP_GRAPHS_base = py-deps-all py-deps-swh py-deps-ext
 DEP_GRAPHS += $(patsubst %,%.dot,$(DEP_GRAPHS_base))
 DEP_GRAPHS += $(patsubst %,%.pdf,$(DEP_GRAPHS_base))
 DEP_GRAPHS += $(patsubst %,%.svg,$(DEP_GRAPHS_base))
 PY_DEPGRAPH = ../bin/py-depgraph
 
 UML_DIAGS_SRC = $(wildcard *.uml)
 UML_DIAGS = $(patsubst %.uml,%.svg,$(UML_DIAGS_SRC))
 
 all: $(DEP_GRAPHS) $(UML_DIAGS)
 
 py-deps-all.dot: $(PY_DEPGRAPH) $(PY_REQUIREMENTS)
 	cd ../../.. ; $(CURDIR)/$(PY_DEPGRAPH) > $(CURDIR)/$@
 
 py-deps-swh.dot: $(PY_DEPGRAPH) $(PY_REQUIREMENTS)
 	cd ../../.. ; $(CURDIR)/$(PY_DEPGRAPH) --no-external > $(CURDIR)/$@
 
 py-deps-ext.dot: $(PY_DEPGRAPH) $(PY_REQUIREMENTS)
 	cd ../../.. ; $(CURDIR)/$(PY_DEPGRAPH) --no-internal > $(CURDIR)/$@
 
 %.pdf: %.dot
 	dot -T pdf $< > $@
 
 %.svg: %.dot
 	dot -T svg $< > $@
 
 %.svg: %.uml
-	plantuml -tsvg $<
+	DISPLAY="" plantuml -tsvg $<
 
 clean:
 	-rm -f $(DEP_GRAPHS) $(UML_DIAGS)