diff --git a/dlls/ntdll/unix/system.c b/dlls/ntdll/unix/system.c
index faa7532cfef..8add2cabd4f 100644
--- a/dlls/ntdll/unix/system.c
+++ b/dlls/ntdll/unix/system.c
@@ -538,8 +538,8 @@ static DWORD count_bits(ULONG_PTR mask)
     DWORD count = 0;
     while (mask > 0)
     {
+        if (mask & 1) ++count;
         mask >>= 1;
-        count++;
     }
     return count;
 }