diff --git a/test/lib/library.exp b/test/lib/library.exp
index 75bf921c..4ec0e697 100644
--- a/test/lib/library.exp
+++ b/test/lib/library.exp
@@ -846,7 +846,7 @@ proc save_env {{file ""}} {
 # @param string  File to save the environment to.  Default is "$TESTDIR/tmp/env1~".
 # @see assert_env_unmodified()
 proc _save_env {{file ""}} {
-    assert_bash_exec "{ set; declare -F; shopt -p; } > \"$file\""
+    assert_bash_exec "{ (set -o posix ; set); declare -F; shopt -p; } > \"$file\""
 }