diff --git a/AMSS_NCKU_source/makefile b/AMSS_NCKU_source/makefile
index ba12c5b..59eeacb 100644
--- a/AMSS_NCKU_source/makefile
+++ b/AMSS_NCKU_source/makefile
@@ -95,6 +95,7 @@ CFILES_CUDA = bssn_rhs_cuda.o
 ## RK4 kernel switch (independent from USE_CXX_KERNELS)
 ifeq ($(USE_CXX_RK4),1)
 CFILES += rungekutta4_rout_c.o
+CFILES_CUDA += rungekutta4_rout_c.o
 RK4_F90_OBJ =
 else
 RK4_F90_OBJ = rungekutta4_rout.o