diff --git a/Source/cmJSONHelpers.h b/Source/cmJSONHelpers.h
index fe5dca588d..b35825dc57 100644
--- a/Source/cmJSONHelpers.h
+++ b/Source/cmJSONHelpers.h
@@ -348,7 +348,7 @@ struct cmJSONHelperBuilder
         if (!func(t, &(*value)[key], state)) {
           success = false;
         }
-        out[key] = std::move(t);
+        out.emplace(key, std::move(t));
         state->pop_stack();
       }
       return success;