diff --git a/ggml/src/ggml.c b/ggml/src/ggml.c
index 3841a594cf..df9ac34b4e 100644
--- a/ggml/src/ggml.c
+++ b/ggml/src/ggml.c
@@ -6741,7 +6741,7 @@ static void ggml_compute_backward(
         } break;
         case GGML_OP_SUM: {
             if (src0_needs_grads) {
-                ggml_add_or_set(ctx, cgraph, isrc0, grad);
+                ggml_add_or_set(ctx, cgraph, isrc0, ggml_repeat(ctx, grad, src0));
             }
         } break;
         case GGML_OP_SUM_ROWS: {