diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 6d2a69652c39..bbde8d3d6c8a 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -2790,6 +2790,12 @@ static struct hist_field *parse_unary(struct hist_trigger_data *hist_data,
 		ret = PTR_ERR(operand1);
 		goto free;
 	}
+	if (operand1->flags & HIST_FIELD_FL_STRING) {
+		/* String type can not be the operand of unary operator. */
+		destroy_hist_field(operand1, 0);
+		ret = -EINVAL;
+		goto free;
+	}
 
 	expr->flags |= operand1->flags &
 		(HIST_FIELD_FL_TIMESTAMP | HIST_FIELD_FL_TIMESTAMP_USECS);
@@ -2890,6 +2896,10 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 		operand1 = NULL;
 		goto free;
 	}
+	if (operand1->flags & HIST_FIELD_FL_STRING) {
+		ret = -EINVAL;
+		goto free;
+	}
 
 	/* rest of string could be another expression e.g. b+c in a+b+c */
 	operand_flags = 0;
@@ -2899,6 +2909,10 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
 		operand2 = NULL;
 		goto free;
 	}
+	if (operand2->flags & HIST_FIELD_FL_STRING) {
+		ret = -EINVAL;
+		goto free;
+	}
 
 	ret = check_expr_operands(operand1, operand2);
 	if (ret)