diff --git a/libisofs/filters/external.c b/libisofs/filters/external.c
index 78456cb..b724a84 100644
--- a/libisofs/filters/external.c
+++ b/libisofs/filters/external.c
@@ -620,7 +620,7 @@ int iso_file_add_external_filter(IsoFile *file, IsoExternalFilterCommand *cmd,
     if (cmd->behavior & (2 | 4)) {
         original_size = iso_file_get_size(file);
         if (original_size <= 0 ||
-            ((cmd->behavior & 4) && original_size < 2048)) {
+            ((cmd->behavior & 4) && original_size <= 2048)) {
             return 2;
         }
     }
diff --git a/libisofs/libisofs.h b/libisofs/libisofs.h
index 804cc42..9b83bbf 100644
--- a/libisofs/libisofs.h
+++ b/libisofs/libisofs.h
@@ -4714,7 +4714,7 @@ struct iso_external_filter_command
      * bit2= Do not install filter if the number of output blocks is
      *       not smaller than the number of input blocks. Block size is 2048.
      *       Assume that non-empty input yields non-empty output and thus do
-     *       not attempt to attach a filter to files smaller than 2048 bytes.
+     *       not attempt to attach a filter to files smaller than 2049 bytes.
      */
     int behavior;
 };