diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index bcdde0a1a..e6bccb90e 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -49,9 +49,9 @@ double GetDifficulty(const CBlockIndex* blockindex)
 {
     // Floating point number that is a multiple of the minimum difficulty,
     // minimum difficulty = 1.0.
-    if (blockindex == NULL)
+    if (blockindex == nullptr)
     {
-        if (chainActive.Tip() == NULL)
+        if (chainActive.Tip() == nullptr)
             return 1.0;
         else
             blockindex = chainActive.Tip();