diff --git a/src/fish_tests.cpp b/src/fish_tests.cpp
index f875438d4..fc2b2caba 100644
--- a/src/fish_tests.cpp
+++ b/src/fish_tests.cpp
@@ -1154,7 +1154,7 @@ static void test_utf8()
     wchar_t w4[] = {0x15555, 0xf7777, 0xa};
     wchar_t w5[] = {0x255555, 0x1fa04ff, 0xddfd04, 0xa};
     wchar_t w6[] = {0xf255555, 0x1dfa04ff, 0x7fddfd04, 0xa};
-    wchar_t wb[] = {-2, 0xa, (wchar_t)0xffffffff, 0x0441};
+    wchar_t wb[] = {(wchar_t)-2, 0xa, (wchar_t)0xffffffff, 0x0441};
     wchar_t wm[] = {0x41, 0x0441, 0x3042, 0xff67, 0x9b0d, 0x2e05da67};
     wchar_t wb1[] = {0xa, 0x0422};
     wchar_t wb2[] = {0xd800, 0xda00, 0x41, 0xdfff, 0xa};