diff --git a/fs/Vfat.cpp b/fs/Vfat.cpp
index 7bd05ec..7338c1e 100644
--- a/fs/Vfat.cpp
+++ b/fs/Vfat.cpp
@@ -164,7 +164,7 @@
     return rc;
 }
 
-status_t Format(const std::string& source, unsigned int numSectors) {
+status_t Format(const std::string& source, unsigned long numSectors) {
     std::vector<std::string> cmd;
     cmd.push_back(kMkfsPath);
     cmd.push_back("-F");
@@ -177,7 +177,7 @@
 
     if (numSectors) {
         cmd.push_back("-s");
-        cmd.push_back(StringPrintf("%u", numSectors));
+        cmd.push_back(StringPrintf("%lu", numSectors));
     }
 
     cmd.push_back(source);