diff --git a/examples_ptx/common_gpu.mk b/examples_ptx/common_gpu.mk
index e02e5b95..313768e8 100644
--- a/examples_ptx/common_gpu.mk
+++ b/examples_ptx/common_gpu.mk
@@ -5,7 +5,7 @@ CXX=g++ -ffast-math
 CXXFLAGS=-O3 -I$(CUDATK)/include -Iobjs_gpu/ -D_CUDA_
 #
 NVCC=nvcc
-NVCC_FLAGS=-O3 -arch=sm_35 -D_CUDA_ -I../ -Xptxas=-v -Iobjs_gpu/
+NVCC_FLAGS+=-O3 -arch=sm_35 -D_CUDA_ -I../ -Xptxas=-v -Iobjs_gpu/
 ifdef PTXCC_REGMAX
   NVCC_FLAGS += --maxrregcount=$(PTXCC_REGMAX)
 endif
diff --git a/examples_ptx/radixSort/Makefile_gpu b/examples_ptx/radixSort/Makefile_gpu
index 4e101992..ad48a011 100644
--- a/examples_ptx/radixSort/Makefile_gpu
+++ b/examples_ptx/radixSort/Makefile_gpu
@@ -1,6 +1,8 @@
 PROG=radixSort
 ISPC_SRC=radixSort.ispc
+
 CU_SRC=radixSort.cu
+NVCC_FLAGS=-Xptxas=-O1
 CXX_SRC=radixSort.cpp  radixSort.cpp
 PTXCC_REGMAX=64