diff --git a/pkg/tools/toolloop.go b/pkg/tools/toolloop.go
index ac568f598..5cbf5662a 100644
--- a/pkg/tools/toolloop.go
+++ b/pkg/tools/toolloop.go
@@ -132,7 +132,11 @@ func RunToolLoop(
 			Content: response.Content,
 		}
 		for _, tc := range normalizedToolCalls {
-			argumentsJSON, _ := json.Marshal(tc.Arguments)
+			argumentsJSON, err := json.Marshal(tc.Arguments)
+			if err != nil {
+				logger.Warnf("toolloop: failed to marshal tool call arguments for %s: %v", tc.Name, err)
+				argumentsJSON = []byte("{}")
+			}
 			assistantMsg.ToolCalls = append(assistantMsg.ToolCalls, providers.ToolCall{
 				ID:        tc.ID,
 				Type:      "function",