diff --git a/audio.experimental.a-lec.org/Makefile.am b/audio.experimental.a-lec.org/Makefile.am
index 1e8cc4a..3cab3f3 100644
--- a/audio.experimental.a-lec.org/Makefile.am
+++ b/audio.experimental.a-lec.org/Makefile.am
@@ -89,7 +89,7 @@ mumble-vm.img: $(IMAGE_SOURCE)
 			--image-type=mbr-raw \
 			--image-size=6G mumble-vm-system.scm` \
 		$@
-build:
+build: $(IMAGE_SOURCE)
 	guix system build \
 		--image-type=mbr-raw \
 		--image-size=6G mumble-vm-system.scm