diff --git a/t/test-lib.sh b/t/test-lib.sh
index dff5e25ae6c..830e5e73603 100644
--- a/t/test-lib.sh
+++ b/t/test-lib.sh
@@ -620,7 +620,18 @@ test_path_is_missing () {
 
 test_must_fail () {
 	"$@"
-	test $? -gt 0 -a $? -le 129 -o $? -gt 192
+	exit_code=$?
+	if test $exit_code = 0; then
+		echo >&2 "test_must_fail: command succeeded: $*"
+		return 1
+	elif test $exit_code -gt 129 -a $exit_code -le 192; then
+		echo >&2 "test_must_fail: died by signal: $*"
+		return 1
+	elif test $exit_code = 127; then
+		echo >&2 "test_must_fail: command not found: $*"
+		return 1
+	fi
+	return 0
 }
 
 # Similar to test_must_fail, but tolerates success, too.  This is
@@ -636,7 +647,15 @@ test_must_fail () {
 
 test_might_fail () {
 	"$@"
-	test $? -ge 0 -a $? -le 129 -o $? -gt 192
+	exit_code=$?
+	if test $exit_code -gt 129 -a $exit_code -le 192; then
+		echo >&2 "test_might_fail: died by signal: $*"
+		return 1
+	elif test $exit_code = 127; then
+		echo >&2 "test_might_fail: command not found: $*"
+		return 1
+	fi
+	return 0
 }
 
 # test_cmp is a helper function to compare actual and expected output.