diff --git a/quickjs.c b/quickjs.c
index f0372eb..bce0fd6 100644
--- a/quickjs.c
+++ b/quickjs.c
@@ -45114,7 +45114,7 @@ JSPromiseStateEnum JS_PromiseState(JSContext *ctx, JSValue promise)
 {
     JSPromiseData *s = JS_GetOpaque(promise, JS_CLASS_PROMISE);
     if (!s)
-        return -1;
+      return JS_INVALID_PROMISE_STATE;
     return s->promise_state;
 }
 
diff --git a/quickjs.h b/quickjs.h
index 453e03d..96414c8 100644
--- a/quickjs.h
+++ b/quickjs.h
@@ -977,13 +977,17 @@ JS_EXTERN int JS_SetModuleExportList(JSContext *ctx, JSModuleDef *m,
 
 /* Promise */
 
+#define JS_INVALID_PROMISE_STATE -1
+
 typedef enum JSPromiseStateEnum {
     JS_PROMISE_PENDING,
     JS_PROMISE_FULFILLED,
     JS_PROMISE_REJECTED,
 } JSPromiseStateEnum;
 
+/* Returns JSPromiseReactionEnum for the promise or JS_INVALID_PROMISE_STATE if the value is not a promise. */
 JS_EXTERN JSPromiseStateEnum JS_PromiseState(JSContext *ctx, JSValue promise);
+/* Return the result of the promise if the promise's state is in the FULFILLED or REJECTED state. Otherwise returns JS_UNDEFINED. */
 JS_EXTERN JSValue JS_PromiseResult(JSContext *ctx, JSValue promise);
 
 /* Version */