diff --git a/drivers/infiniband/hw/mlx5/main.c b/drivers/infiniband/hw/mlx5/main.c
index 0ebd3c7b2d2a..aa7a44ea49fa 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -2095,7 +2095,7 @@ static inline char *mmap_cmd2str(enum mlx5_ib_mmap_cmd cmd)
 	case MLX5_IB_MMAP_DEVICE_MEM:
 		return "Device Memory";
 	default:
-		return NULL;
+		return "Unknown";
 	}
 }