diff --git a/components/script/dom/bindings/conversions.rs b/components/script/dom/bindings/conversions.rs
index 15087fe5a0f..cd092814e0a 100644
--- a/components/script/dom/bindings/conversions.rs
+++ b/components/script/dom/bindings/conversions.rs
@@ -221,6 +221,7 @@ impl FromJSValConvertible for DOMString {
 /// Convert the given `JSString` to a `DOMString`. Fails if the string does not
 /// contain valid UTF-16.
 pub unsafe fn jsstring_to_str(cx: *mut JSContext, s: *mut JSString) -> DOMString {
+    assert!(!s.is_null());
     let latin1 = JS_DeprecatedStringHasLatin1Chars(s);
     DOMString::from_string(if latin1 {
         latin1_to_string(cx, s)
diff --git a/components/script/dom/console.rs b/components/script/dom/console.rs
index f1e21b5897b..ae041dfa7da 100644
--- a/components/script/dom/console.rs
+++ b/components/script/dom/console.rs
@@ -73,6 +73,9 @@ where
 unsafe fn handle_value_to_string(cx: *mut jsapi::JSContext, value: HandleValue) -> DOMString {
     rooted!(in(cx) let mut js_string = std::ptr::null_mut::<jsapi::JSString>());
     js_string.set(JS_ValueToSource(cx, value));
+    if js_string.is_null() {
+        return "<error converting value to string>".into();
+    }
     jsstring_to_str(cx, *js_string)
 }