diff --git a/libisofs/filters/external.c b/libisofs/filters/external.c
index 4462953..78456cb 100644
--- a/libisofs/filters/external.c
+++ b/libisofs/filters/external.c
@@ -615,7 +615,15 @@ int iso_file_add_external_filter(IsoFile *file, IsoExternalFilterCommand *cmd,
     int ret;
     FilterContext *f = NULL;
     IsoStream *stream;
+    off_t original_size = 0, filtered_size = 0;
 
+    if (cmd->behavior & (2 | 4)) {
+        original_size = iso_file_get_size(file);
+        if (original_size <= 0 ||
+            ((cmd->behavior & 4) && original_size < 2048)) {
+            return 2;
+        }
+    }
     ret = extf_create_context(cmd, &f, 0);
     if (ret < 0) {
         return ret;
@@ -627,10 +635,18 @@ int iso_file_add_external_filter(IsoFile *file, IsoExternalFilterCommand *cmd,
     }
     /* Run a full filter process getsize so that the size is cached */
     stream = iso_file_get_stream(file);
-    ret = iso_stream_get_size(stream);
+    filtered_size = iso_stream_get_size(stream);
     if (ret < 0) {
         return ret;
     }
+    if (((cmd->behavior & 2) && filtered_size >= original_size) ||
+        ((cmd->behavior & 4) && filtered_size / 2048 >= original_size / 2048)){
+        ret = iso_file_remove_filter(file, 0);
+        if (ret < 0) {
+            return ret;
+        }
+        return 2;
+    }
     return ISO_SUCCESS;
 }
 
diff --git a/libisofs/libisofs.h b/libisofs/libisofs.h
index 17c2ec8..804cc42 100644
--- a/libisofs/libisofs.h
+++ b/libisofs/libisofs.h
@@ -4710,7 +4710,11 @@ struct iso_external_filter_command
 
     /* A bit field which controls behavior variations:
      * bit0= Shortcut: 0 sized input will surely yield 0 sized output
-     * >>> not implemented yet: bit1= Do not install filter if the output becomes larger than the input
+     * bit1= Do not install filter if the output is not smaller than the input
+     * 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.
      */
     int behavior;
 };