diff --git a/src/io.c b/src/io.c
index 40132b0..f3b1cb1 100644
--- a/src/io.c
+++ b/src/io.c
@@ -667,8 +667,7 @@ find_identical_ends (struct file_data filevec[])
     {
       middle_guess = guess_lines (0, 0, p0 - filevec[0].prefix_end);
       lin suffix_guess = guess_lines (0, 0, buffer0 + n0 - p0);
-      for (prefix_count = 1;  prefix_count <= context;  prefix_count *= 2)
-        continue;
+      prefix_count = (lin) 1 << (floor_log2 (context) + 1);
       alloc_lines0 = (prefix_count + middle_guess
                       + MIN (context, suffix_guess));
     }