diff --git a/nvflare/app_common/shareablegenerators/full_model_shareable_generator.py b/nvflare/app_common/shareablegenerators/full_model_shareable_generator.py
index 5cd83258d88..bee45b7826d 100644
--- a/nvflare/app_common/shareablegenerators/full_model_shareable_generator.py
+++ b/nvflare/app_common/shareablegenerators/full_model_shareable_generator.py
@@ -57,7 +57,7 @@ def shareable_to_learnable(self, shareable: Shareable, fl_ctx: FLContext) -> Mod
             if dxo.data is not None:
                 model_diff = dxo.data
                 for v_name, v_value in model_diff.items():
-                    weights[v_name] += v_value
+                    weights[v_name] = weights[v_name] + v_value
         elif dxo.data_kind == DataKind.WEIGHTS:
             weights = dxo.data
             if not weights: