diff --git a/makefiles/tools.mk b/makefiles/tools.mk
index 03aeb9d..b1bab03 100644
--- a/makefiles/tools.mk
+++ b/makefiles/tools.mk
@@ -35,7 +35,7 @@
 ## --interactive: Attach streams if running interactively (!jenkins)
 ## --tty        : Attach stdout else jenkins::docker is silent.
 ## -----------------------------------------------------------------------
-is-stdin       = $(shell test -t 0 && { echo '--interactive' })
+is-stdin       = $(shell test -t 0 && { echo '--interactive'; })
 is-stdin       += --tty
 
 # Docker volume mounts: container:/app/release <=> localhost:{pwd}/release