diff --git a/src/module/os.c b/src/module/os.c
index c13cd33f..f31ca488 100644
--- a/src/module/os.c
+++ b/src/module/os.c
@@ -82,7 +82,7 @@ void platformIsPosix(WrenVM* vm)
   #elif defined(_POSIX_VERSION)
     wrenSetSlotBool(vm, 0, true);
   #else
-    wrenSetSlotString(vm, 0, false);
+    wrenSetSlotBool(vm, 0, false);
   #endif
 }