diff --git a/doc/ffmpeg.texi b/doc/ffmpeg.texi
index 4616a42..de6d3f1 100644
--- a/doc/ffmpeg.texi
+++ b/doc/ffmpeg.texi
@@ -996,7 +996,7 @@ such streams is attempted.
 Allow input streams with unknown type to be copied instead of failing if copying
 such streams is attempted.
 
-@item -map_channel [@var{input_file_id}.@var{stream_specifier}.@var{channel_id}|-1][:@var{output_file_id}.@var{stream_specifier}]
+@item -map_channel [@var{input_file_id}.@var{stream_specifier}.@var{channel_id}|-1][?][:@var{output_file_id}.@var{stream_specifier}]
 Map an audio channel from a given input to an output. If
 @var{output_file_id}.@var{stream_specifier} is not set, the audio channel will
 be mapped on all the audio streams.
@@ -1005,6 +1005,10 @@ Using "-1" instead of
 @var{input_file_id}.@var{stream_specifier}.@var{channel_id} will map a muted
 channel.
 
+A trailing @code{?} will allow the map_channel to be
+optional: if the map_channel matches no channel the map_channel will be ignored instead
+of failing.
+
 For example, assuming @var{INPUT} is a stereo audio file, you can switch the
 two audio channels with the following command:
 @example
@@ -1052,6 +1056,13 @@ video stream), you can use the following command:
 ffmpeg -i input.mkv -filter_complex "[0:1] [0:2] amerge" -c:a pcm_s16le -c:v copy output.mkv
 @end example
 
+To map the first two audio channels from the first input, and using the
+trailing @code{?}, ignore the audio channel mapping if the first input is
+mono instead of stereo:
+@example
+ffmpeg -i INPUT -map_channel 0.0.0 -map_channel 0.0.1? OUTPUT
+@end example
+
 @item -map_metadata[:@var{metadata_spec_out}] @var{infile}[:@var{metadata_spec_in}] (@emph{output,per-metadata})
 Set metadata information of the next output file from @var{infile}. Note that
 those are file indices (zero-based), not filenames.
diff --git a/ffmpeg_opt.c b/ffmpeg_opt.c
index 1c4a11e..2f6bfc9 100644
--- a/ffmpeg_opt.c
+++ b/ffmpeg_opt.c
@@ -405,6 +405,11 @@ static int opt_map_channel(void *optctx, const char *opt, const char *arg)
     int n;
     AVStream *st;
     AudioChannelMap *m;
+    char *allow_unused;
+    char *mapchan;
+    mapchan = av_strdup(arg);
+    if (!mapchan)
+        return AVERROR(ENOMEM);
 
     GROW_ARRAY(o->audio_channel_maps, o->nb_audio_channel_maps);
     m = &o->audio_channel_maps[o->nb_audio_channel_maps - 1];
@@ -450,10 +455,20 @@ static int opt_map_channel(void *optctx, const char *opt, const char *arg)
                m->file_idx, m->stream_idx);
         exit_program(1);
     }
+    /* allow trailing ? to map_channel */
+    if (allow_unused = strchr(mapchan, '?'))
+        *allow_unused = 0;
     if (m->channel_idx < 0 || m->channel_idx >= st->codecpar->channels) {
-        av_log(NULL, AV_LOG_FATAL, "mapchan: invalid audio channel #%d.%d.%d\n",
-               m->file_idx, m->stream_idx, m->channel_idx);
-        exit_program(1);
+        if (allow_unused) {
+            av_log(NULL, AV_LOG_VERBOSE, "mapchan: invalid audio channel #%d.%d.%d\n",
+                    m->file_idx, m->stream_idx, m->channel_idx);
+        } else {
+            av_log(NULL, AV_LOG_FATAL,  "mapchan: invalid audio channel #%d.%d.%d\n"
+                    "To ignore this, add a trailing '?' to the map_channel.\n",
+                    m->file_idx, m->stream_idx, m->channel_idx);
+            exit_program(1);
+        }
+
     }
     return 0;
 }
diff --git a/tests/fate/ffmpeg.mak b/tests/fate/ffmpeg.mak
index 0ec5a34..f3fbc84 100644
--- a/tests/fate/ffmpeg.mak
+++ b/tests/fate/ffmpeg.mak
@@ -10,6 +10,14 @@ FATE_MAPCHAN-$(CONFIG_CHANNELMAP_FILTER) += fate-mapchan-silent-mono
 fate-mapchan-silent-mono: tests/data/asynth-22050-1.wav
 fate-mapchan-silent-mono: CMD = md5 -i $(TARGET_PATH)/tests/data/asynth-22050-1.wav -map_channel -1 -map_channel 0.0.0 -fflags +bitexact -f wav
 
+FATE_MAPCHAN-$(CONFIG_CHANNELMAP_FILTER) += fate-mapchan-2ch-extract-ch0-ch2-trailing
+fate-mapchan-2ch-extract-ch0-ch2-trailing: tests/data/asynth-44100-2.wav
+fate-mapchan-2ch-extract-ch0-ch2-trailing: CMD = md5 -i $(TARGET_PATH)/tests/data/asynth-44100-2.wav -map_channel 0.0.0 -map_channel 0.0.2? -fflags +bitexact -f wav
+
+FATE_MAPCHAN-$(CONFIG_CHANNELMAP_FILTER) += fate-mapchan-3ch-extract-ch0-ch2-trailing
+fate-mapchan-3ch-extract-ch0-ch2-trailing: tests/data/asynth-44100-3.wav
+fate-mapchan-3ch-extract-ch0-ch2-trailing: CMD = md5 -i $(TARGET_PATH)/tests/data/asynth-44100-3.wav -map_channel 0.0.0 -map_channel 0.0.2? -fflags +bitexact -f wav
+
 FATE_MAPCHAN = $(FATE_MAPCHAN-yes)
 
 FATE_FFMPEG += $(FATE_MAPCHAN)
diff --git a/tests/ref/fate/mapchan-2ch-extract-ch0-ch2-trailing b/tests/ref/fate/mapchan-2ch-extract-ch0-ch2-trailing
new file mode 100644
index 0000000..a540037
--- /dev/null
+++ b/tests/ref/fate/mapchan-2ch-extract-ch0-ch2-trailing
@@ -0,0 +1 @@
+b6e1d142b4e484221562e7b66b9bbbdc
diff --git a/tests/ref/fate/mapchan-3ch-extract-ch0-ch2-trailing b/tests/ref/fate/mapchan-3ch-extract-ch0-ch2-trailing
new file mode 100644
index 0000000..6237a98
--- /dev/null
+++ b/tests/ref/fate/mapchan-3ch-extract-ch0-ch2-trailing
@@ -0,0 +1 @@
+ae533985186cab287309c04f6b3e866c
