diff --git a/cmdline/main.c b/cmdline/main.c
index aa6deea3..5918d5e9 100644
--- a/cmdline/main.c
+++ b/cmdline/main.c
@@ -42,6 +42,9 @@ static int build_spindown_argv(int argc, char* argv[], char* spindown_argv[5])
 
 static int needs_quote(const WCHAR* arg)
 {
+	if (*arg == 0)
+		return 1;
+
 	while (*arg) {
 		if (*arg == L' ' || *arg == L'\t' || *arg == L'"')
 			return 1;
diff --git a/os/mingw.c b/os/mingw.c
index 067a455f..6a6fa74d 100644
--- a/os/mingw.c
+++ b/os/mingw.c
@@ -2493,6 +2493,9 @@ int windows_join(thread_id_t thread, void** retval)
 
 static int needs_quote(const WCHAR* arg)
 {
+	if (*arg == 0)
+		return 1;
+
 	while (*arg) {
 		if (*arg == L' ' || *arg == L'\t' || *arg == L'"')
 			return 1;