diff --git a/libisofs/filters/external.c b/libisofs/filters/external.c
index b724a84..36dddb7 100644
--- a/libisofs/filters/external.c
+++ b/libisofs/filters/external.c
@@ -46,7 +46,11 @@ typedef struct
     int out_eof;
     uint8_t pipebuf[2048]; /* buffers in case of EAGAIN on write() */
     int pipebuf_fill;
+
+#ifdef Libisofs_extf_old_behavior_bit_0
     int is_0_run;
+#endif
+
 } ExternalFilterRuntime;
 
 
@@ -68,7 +72,11 @@ int extf_running_new(ExternalFilterRuntime **running, int send_fd, int recv_fd,
     o->out_eof = 0;
     memset(o->pipebuf, 0, sizeof(o->pipebuf));
     o->pipebuf_fill = 0;
+
+#ifdef Libisofs_extf_old_behavior_bit_0
     o->is_0_run = 0;
+#endif
+
     return 1;
 }
 
@@ -124,6 +132,8 @@ int extf_stream_open_flag(IsoStream *stream, int flag)
     if (data->running != NULL) {
         return ISO_FILE_ALREADY_OPENED;
     }
+
+#ifdef Libisofs_extf_old_behavior_bit_0
     if (data->cmd->behavior & 1) {
         if (iso_stream_get_size(data->orig) == 0) {
             /* Do not fork. Place message for .read and .close */;
@@ -136,6 +146,8 @@ int extf_stream_open_flag(IsoStream *stream, int flag)
             return 1;
         }
     }
+#endif /* Libisofs_extf_old_behavior_bit_0 */
+
     if (data->size < 0 && !(flag & 1)) {
         /* Do the size determination run now, so that the size gets cached
            and .get_size() will not fail on an opened stream.
@@ -167,31 +179,11 @@ int extf_stream_open_flag(IsoStream *stream, int flag)
 
     if (child_pid != 0) {
         /* parent */
-
-#ifndef NIX
         ret = extf_running_new(&running, send_pipe[1], recv_pipe[0], child_pid,
                                0);
         if (ret < 0) {
             goto parent_failed;
         }
-#else
-        running = calloc(sizeof(ExternalFilterRuntime), 1);
-        if (running == NULL) {
-            ret = ISO_OUT_OF_MEM;
-            goto parent_failed;
-        }
-        running->send_fd = send_pipe[1];
-        running->recv_fd = recv_pipe[0];
-        running->pid = child_pid;
-        running->in_counter = 0;
-        running->in_eof = 0;
-        running->out_counter = 0;
-        running->out_eof = 0;
-        memset(running->pipebuf, 0, sizeof(running->pipebuf));
-        running->pipebuf_fill = 0;
-        running->is_0_run = 0;
-#endif /* NIX */
-
         data->running = running;
 
         /* Give up the child-side pipe ends */
@@ -267,7 +259,12 @@ int extf_stream_open(IsoStream *stream)
 static
 int extf_stream_close(IsoStream *stream)
 {
-    int ret, status, is_0_run;
+    int ret, status;
+
+#ifdef Libisofs_extf_old_behavior_bit_0
+    int is_0_run;
+#endif
+
     ExternalFilterStreamData *data;
 
     if (stream == NULL) {
@@ -278,8 +275,12 @@ int extf_stream_close(IsoStream *stream)
     if (data->running == NULL) {
         return 1;
     }
+
+#ifdef Libisofs_extf_old_behavior_bit_0
     is_0_run = data->running->is_0_run;
     if (!is_0_run) {
+#endif
+
         if(data->running->recv_fd != -1)
             close(data->running->recv_fd);
         if(data->running->send_fd != -1)
@@ -290,11 +291,19 @@ int extf_stream_close(IsoStream *stream)
             kill(data->running->pid, SIGKILL);
             waitpid(data->running->pid, &status, 0);
         }
+
+#ifdef Libisofs_extf_old_behavior_bit_0
     }
+#endif
+
     free(data->running);
     data->running = NULL;
+
+#ifdef Libisofs_extf_old_behavior_bit_0
     if (is_0_run)
         return 1;
+#endif
+
     return iso_stream_close(data->orig);
 }
 
@@ -315,7 +324,13 @@ int extf_stream_read(IsoStream *stream, void *buf, size_t desired)
     if (running == NULL) {
         return ISO_FILE_NOT_OPENED;
     }
+
+#ifdef Libisofs_extf_old_behavior_bit_0
     if (running->out_eof || running->is_0_run) {
+#else
+    if (running->out_eof) {
+#endif
+
         return 0;
     }
 
@@ -617,7 +632,11 @@ int iso_file_add_external_filter(IsoFile *file, IsoExternalFilterCommand *cmd,
     IsoStream *stream;
     off_t original_size = 0, filtered_size = 0;
 
+#ifdef Libisofs_extf_old_behavior_bit_0
     if (cmd->behavior & (2 | 4)) {
+#else
+    if (cmd->behavior & (1 | 2 | 4)) {
+#endif
         original_size = iso_file_get_size(file);
         if (original_size <= 0 ||
             ((cmd->behavior & 4) && original_size <= 2048)) {
diff --git a/libisofs/libisofs.h b/libisofs/libisofs.h
index 8d3d0ee..f2c347d 100644
--- a/libisofs/libisofs.h
+++ b/libisofs/libisofs.h
@@ -4709,8 +4709,14 @@ struct iso_external_filter_command
     char **argv;
 
     /* A bit field which controls behavior variations:
+
+#ifdef Libisofs_extf_old_behavior_bit_0
      * bit0= Shortcut: 0 sized input will surely yield 0 sized output
-     * bit1= Do not install filter if the output is not smaller than the input
+#else
+     * bit0= Do not install filter if the input has size 0.
+#endif
+
+     * 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