diff --git a/GNUmakefile b/GNUmakefile
index addf002..959a943 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -1,3 +1,4 @@
+SHELL := bash
 .SHELLFLAGS := -eu -o pipefail -c
 .ONESHELL:
 .DELETE_ON_ERROR: