diff --git a/test/test-lib.sh b/test/test-lib.sh
index c81c709..5ed6a96 100755
--- a/test/test-lib.sh
+++ b/test/test-lib.sh
@@ -844,7 +844,12 @@ test_emacs () {
 	if [ -z "$EMACS_SERVER" ]; then
 		EMACS_SERVER="notmuch-test-suite-$$"
 		# start a detached screen session with an emacs server
-		screen -S "$EMACS_SERVER" -d -m "$TMP_DIRECTORY/run_emacs" \
+		# The emacs server places its socket in TMPDIR, but ld.so unsets
+		# TMPDIR when loading setgid binaries like screen, so we must
+		# explicitly pass TMPDIR through to emacs.
+		screen -S "$EMACS_SERVER" -d -m \
+		    env TMPDIR="$TMPDIR" \
+		    "$TMP_DIRECTORY/run_emacs" \
 			--no-window-system \
 			--eval "(setq server-name \"$EMACS_SERVER\")" \
 			--eval '(server-start)' \