diff --git a/src/main.cpp b/src/main.cpp
index ed17bdee9..e748605a5 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -5917,8 +5917,7 @@ void FindFilesToPrune(std::set<int>& setFilesToPrune)
 bool CheckDiskSpace(uint64_t nAdditionalBytes)
 {
     uint64_t nFreeBytesAvailable = boost::filesystem::space(GetDataDir()).available;
-
-    fprintf(stderr,"Free bytes on disk: %d\n", nFreeBytesAvailable);
+    fprintf(stderr,"Free bytes on disk: %lu\n", nFreeBytesAvailable);
     // Check for nMinDiskSpace bytes (currently 50MB)
     if (nFreeBytesAvailable < nMinDiskSpace + nAdditionalBytes)
         return AbortNode("Disk space is low!", _("Error: Disk space is low!"));