diff --git a/t/README b/t/README
index 1dc908e43a..76a0daa3ac 100644
--- a/t/README
+++ b/t/README
@@ -84,9 +84,9 @@ appropriately before running "make".
 
 -x::
 	Turn on shell tracing (i.e., `set -x`) during the tests
-	themselves. Implies `--verbose`. Note that this can cause
-	failures in some tests which redirect and test the
-	output of shell functions. Use with caution.
+	themselves. Implies `--verbose`. Note that in non-bash shells,
+	this can cause failures in some tests which redirect and test
+	the output of shell functions. Use with caution.
 
 -d::
 --debug::
diff --git a/t/test-lib.sh b/t/test-lib.sh
index 286c5f33d1..0055ebba46 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -322,6 +322,19 @@ else
 	exec 4>/dev/null 3>/dev/null
 fi
 
+# Send any "-x" output directly to stderr to avoid polluting tests
+# which capture stderr. We can do this unconditionally since it
+# has no effect if tracing isn't turned on.
+#
+# Note that this sets up the trace fd as soon as we assign the variable, so it
+# must come after the creation of descriptor 4 above. Likewise, we must never
+# unset this, as it has the side effect of closing descriptor 4, which we
+# use to show verbose tests to the user.
+#
+# Note also that we don't need or want to export it. The tracing is local to
+# this shell, and we would not want to influence any shells we exec.
+BASH_XTRACEFD=4
+
 test_failure=0
 test_count=0
 test_fixed=0