diff --git a/Makefile b/Makefile
index a851556..74fcc02 100644
--- a/Makefile
+++ b/Makefile
@@ -14,6 +14,7 @@
 DEPLOY_PATH ?= /export/netapp/korap4dnb
 MAX_THREADS ?= 8 # $(shell nproc)
 MAKE ?= make -j $(shell nproc)
+SLACK ?= slack
 KORAPXMLTOOL_HEAP ?= $(shell echo "$$(($(MAX_THREADS) * 2500))")
 KORAPXMLTOOL ?= java -Xmx$(KORAPXMLTOOL_HEAP)m -jar lib/korapxmltool.jar
 MARMOTMALTOOL ?= java -Xmx96000m -jar lib/korapxmltool.jar
@@ -77,9 +78,9 @@
 
 
 %.zip: %.i5.xml
-	tei2korapxml -l warn -s -tk - < $< > $@  || (slack "$@ failed" && false)	
+	tei2korapxml -l warn -s -tk - < $< > $@  || ($(SLACK) "$@ failed" && false)	
 	printf "%s\t%s\n" "$(grep -c '<idsText ' $<)" "$(unzip -l $@ | grep data.xml | wc -l)"
-	slack "$@ created"
+	$(SLACK) "$@ created"
 
 
 %.tree_tagger.zip: %.zip
@@ -112,7 +113,7 @@
 	mkdir -p ${BUILD_DIR}/krill/$(basename $@)
 	mkdir -p $(basename $@)
 	K2K_PUBLISHER_STRING=1 K2K_TRANSLATOR_TEXT=1 korapxml2krill archive --quiet -w -z -cfg krill-korap4dnb.cfg -c ${BUILD_DIR}/krill/$(basename $@)/korapxml2krill.cache -j 30 -te ${BUILD_DIR}/krill/$(basename $@) --non-word-tokens --meta I5 -i $< -i $(word 2,$^) -i $(word 3,$^) -o $(basename $@)
-	slack "$(basename $@) krill archive created"
+	$(SLACK) "$(basename $@) krill archive created"
 
 %.json: %.krill.tar
 	rm -rf $@