diff --git a/tests/buffer_tests.h b/tests/buffer_tests.h
index 315083b..d496d51 100644
--- a/tests/buffer_tests.h
+++ b/tests/buffer_tests.h
@@ -22,16 +22,16 @@
 
 void RunSingleBufferAlignTest(
     size_t max_test_size, void (*test_func)(uint8_t*, size_t),
-    size_t (*set_incr)(size_t) = NULL);
+    size_t (*set_incr)(size_t) = nullptr);
 
 void RunSrcDstBufferAlignTest(
     size_t max_test_size, void (*test_func)(uint8_t*, uint8_t*, size_t),
-    size_t (*set_incr)(size_t) = NULL);
+    size_t (*set_incr)(size_t) = nullptr);
 
 void RunCmpBufferAlignTest(
     size_t max_test_size, void (*test_cmp_func)(uint8_t*, uint8_t*, size_t),
     void (*test_miscmp_func)(uint8_t*, uint8_t*, size_t, size_t),
-    size_t (*set_incr)(size_t) = NULL);
+    size_t (*set_incr)(size_t) = nullptr);
 
 void RunSingleBufferOverreadTest(void (*test_func)(uint8_t*, size_t));