@@ -2,11 +2,16 @@ ifdef FORCE_REBUILD
 	DOCKER_FLAGS = --no-cache --pull
 endif
 
-IMAGE_NAME ?= google/python
+# Note: 'make build/tests/benchmarks' share images by retagging the
+# candidate as 'google/python'.  So this could cause trouble with
+# concurrent builds on the same machine.
+CANDIDATE_NAME ?= $(shell date +%Y-%m-%d_%H_%M)
+IMAGE_NAME ?= google/python:$(CANDIDATE_NAME)
 
 .PHONY: build
 build: build-interpreters
 	docker build $(DOCKER_FLAGS) -t "$(IMAGE_NAME)" .
+	docker tag -f "$(IMAGE_NAME)" "google/python"
 
 .PHONY: build-interpreters
 build-interpreters: