diff --git a/Makefile b/Makefile
index be1cfef..2488165 100644
--- a/Makefile
+++ b/Makefile
@@ -10,6 +10,12 @@
 KALAMAR_INSTANCE ?=
 KALAMAR_INSTANCE_DIR := $(abspath $(KALAMAR_INSTANCE))
 
+# Optional: override the kalamar container image (e.g. a locally built tag).
+# The instance's compose.instance.yaml already defaults to a renderer-capable
+# image; set this to test a specific build, e.g.
+#   make korap KALAMAR_INSTANCE=../Kalamar-Instance-IDS KALAMAR_IMAGE=korap/kalamar:v0.66-alpha-large
+KALAMAR_IMAGE ?=
+
 # Discover all *.i5.xml files in SRC_DIR, excluding inlined tagged copies (*-TAG.i5.xml)
 I5_FILES := $(filter-out %-TAG.i5.xml,$(wildcard $(SRC_DIR)/*.i5.xml))
 BASENAMES := $(patsubst %.i5.xml,%,$(notdir $(I5_FILES)))
@@ -199,7 +205,7 @@
 	java -jar lib/Krill-Indexer.jar -c lib/krill.cfg --progress -i $(subst " ",;,$^) -o $@
 
 korap: check-src $(TARGET_DIR)/index
-	curl -s https://raw.githubusercontent.com/KorAP/KorAP-Docker/master/compose.yaml | sed 's/64543:64543/$(KORAP_PORT):64543/g' | COMPOSE_PROFILES='export,open,lite' INDEX='$(TARGET_DIR)/index' $(if $(KALAMAR_INSTANCE),KALAMAR_INSTANCE_DIR='$(KALAMAR_INSTANCE_DIR)') docker compose -p korap -f - $(if $(KALAMAR_INSTANCE),-f '$(KALAMAR_INSTANCE_DIR)/compose.instance.yaml') up
+	curl -s https://raw.githubusercontent.com/KorAP/KorAP-Docker/master/compose.yaml | sed 's/64543:64543/$(KORAP_PORT):64543/g' | COMPOSE_PROFILES='export,open,lite' INDEX='$(TARGET_DIR)/index' $(if $(KALAMAR_INSTANCE),KALAMAR_INSTANCE_DIR='$(KALAMAR_INSTANCE_DIR)') $(if $(KALAMAR_IMAGE),KALAMAR_IMAGE='$(KALAMAR_IMAGE)') docker compose -p korap -f - $(if $(KALAMAR_INSTANCE),-f '$(KALAMAR_INSTANCE_DIR)/compose.instance.yaml') up
 
 $(TARGET_DIR)/index.tar.xz: $(TARGET_DIR)/index
 	tar -I 'xz -T0' -C $(dir $<) -cf $@ $(notdir $<)