diff --git a/PDP10/kx10_sys.c b/PDP10/kx10_sys.c
index 534942c..8378e0e 100644
--- a/PDP10/kx10_sys.c
+++ b/PDP10/kx10_sys.c
@@ -385,14 +385,16 @@ t_stat load_sblk (FILE *fileref)
        and then comes the data.  Last is a checksum word.  */
     while (get_evac (fileref, &word) == 0 && (word & SMASK)) {
         check = word;
-        count = (int)((((word >> 18) ^ RMASK) + 1) & RMASK);
+        count = (word >> 18) & RMASK;
         addr = word & RMASK;
-        while (count-- > 0) {
+        while (count != 0) {
             if (get_evac (fileref, &word))
                 return SCPE_FMT;
             M[addr++] = word;
             check = (check << 1) + (check >> 35) + word;
             check &= FMASK;
+            count++;
+            count &= RMASK;
         }
         if (get_evac (fileref, &word))
             return SCPE_FMT;