diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index e4ce1121be6..7f36f5beaa6 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -5563,7 +5563,7 @@ JS::AutoSaveExceptionState::~AutoSaveExceptionState()
 }
 
 struct JSExceptionState {
-    JSExceptionState(JSContext *cx) : exception(cx) {}
+    explicit JSExceptionState(JSContext *cx) : exception(cx) {}
     bool throwing;
     PersistentRootedValue exception;
 };