diff --git a/faiss/gpu/test/demo_ivfpq_indexing_gpu.cpp b/faiss/gpu/test/demo_ivfpq_indexing_gpu.cpp
index 1dd52bf0db..f5bee11170 100644
--- a/faiss/gpu/test/demo_ivfpq_indexing_gpu.cpp
+++ b/faiss/gpu/test/demo_ivfpq_indexing_gpu.cpp
@@ -20,7 +20,7 @@
 
 double elapsed() {
     struct timeval tv;
-    gettimeofday(&tv, NULL);
+    gettimeofday(&tv, nullptr);
     return tv.tv_sec + tv.tv_usec * 1e-6;
 }
 
diff --git a/faiss/gpu/utils/Timer.cpp b/faiss/gpu/utils/Timer.cpp
index 0d75b64fc7..f543a08007 100644
--- a/faiss/gpu/utils/Timer.cpp
+++ b/faiss/gpu/utils/Timer.cpp
@@ -14,7 +14,10 @@ namespace faiss {
 namespace gpu {
 
 KernelTimer::KernelTimer(cudaStream_t stream)
-        : startEvent_(0), stopEvent_(0), stream_(stream), valid_(true) {
+        : startEvent_(nullptr),
+          stopEvent_(nullptr),
+          stream_(stream),
+          valid_(true) {
     CUDA_VERIFY(cudaEventCreate(&startEvent_));
     CUDA_VERIFY(cudaEventCreate(&stopEvent_));
 
diff --git a/faiss/gpu/utils/Timer.h b/faiss/gpu/utils/Timer.h
index 7abfa4c903..aa5d65038e 100644
--- a/faiss/gpu/utils/Timer.h
+++ b/faiss/gpu/utils/Timer.h
@@ -18,7 +18,7 @@ class KernelTimer {
    public:
     /// Constructor starts the timer and adds an event into the current
     /// device stream
-    KernelTimer(cudaStream_t stream = 0);
+    KernelTimer(cudaStream_t stream = nullptr);
 
     /// Destructor releases event resources
     ~KernelTimer();