diff --git a/README.rst b/README.rst
index 5bd956f..840cc7f 100644
--- a/README.rst
+++ b/README.rst
@@ -104,7 +104,11 @@
 
 The extra arguments after ``./build.sh B <args>`` is extra deb files to pass to
 sbuild to use as dependencies. In this case, ``librust-A*.deb`` should have
-been built by the previous step.
+been built by the previous step. Alternatively, use the environment variable
+``EXTRA_DEBS``, like so: ::
+
+  $ EXTRA_DEBS=librust-A*.deb ./build.sh B
+  $ EXTRA_DEBS=librust-A.deb,librust-B.deb ./build.sh C
 
 After everything is built successfully, you can ``dput`` all of them and then
 push all the ``pending-*`` branches as normal.
diff --git a/build.sh b/build.sh
index 53e2ccb..d3d5d5e 100755
--- a/build.sh
+++ b/build.sh
@@ -16,6 +16,8 @@
 #     Build using another schroot than debcargo-unstable-amd64-sbuild
 # SBUILD_OPTS=
 #     will pass to sbuild; for example SBUILD_OPTS=--arch=i386
+# EXTRA_DEBS
+#     Include extra dependency debs, e.g. EXTRA_DEBS=librust*.deb.
 set -e
 
 SCRIPTDIR="$(dirname $(readlink -f "$0"))"
@@ -99,8 +101,12 @@
 	fi
 fi
 
-EXTRA_DEBS=( "$@" )
-if [ -n "$*" -a -z "$IGNORE_MISSING_BUILD_DEPS" ]; then
+# allow tab, comma, space as separators
+IFS='	, ' read -r -a EXTRA_DEBS <<< "$EXTRA_DEBS"
+if [ ${#EXTRA_DEBS[@]} -eq 0 ]; then
+	EXTRA_DEBS=( "$@" )
+fi
+if [ ${#EXTRA_DEBS[@]} -ne 0 ]; then
 	IGNORE_MISSING_BUILD_DEPS=1
 	echo >&2 "Given non-empty extra debs; defaulting IGNORE_MISSING_BUILD_DEPS=1"
 fi