diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index 8c2a6324afd7..437b86f021a8 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -6304,12 +6304,19 @@ JS_ReportErrorNumber(JSContext *cx, JSErrorCallback errorCallback,
                      void *userRef, const unsigned errorNumber, ...)
 {
     va_list ap;
-
-    AssertHeapIsIdle(cx);
     va_start(ap, errorNumber);
+    JS_ReportErrorNumberVA(cx, errorCallback, userRef, errorNumber, ap);
+    va_end(ap);
+}
+
+JS_PUBLIC_API(void)
+JS_ReportErrorNumberVA(JSContext *cx, JSErrorCallback errorCallback,
+                       void *userRef, const unsigned errorNumber,
+                       va_list ap)
+{
+    AssertHeapIsIdle(cx);
     js_ReportErrorNumberVA(cx, JSREPORT_ERROR, errorCallback, userRef,
                            errorNumber, JS_TRUE, ap);
-    va_end(ap);
 }
 
 JS_PUBLIC_API(void)
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index f2a11e7331b4..5ebb9cf374eb 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -5650,6 +5650,12 @@ extern JS_PUBLIC_API(void)
 JS_ReportErrorNumber(JSContext *cx, JSErrorCallback errorCallback,
                      void *userRef, const unsigned errorNumber, ...);
 
+#ifdef va_start
+extern JS_PUBLIC_API(void)
+JS_ReportErrorNumberVA(JSContext *cx, JSErrorCallback errorCallback,
+                       void *userRef, const unsigned errorNumber, va_list ap);
+#endif
+
 /*
  * Use an errorNumber to retrieve the format string, args are jschar *
  */