diff --git a/libs/ardour/ardour/types.h b/libs/ardour/ardour/types.h
index 635b78334b..a9b297d505 100644
--- a/libs/ardour/ardour/types.h
+++ b/libs/ardour/ardour/types.h
@@ -543,6 +543,7 @@ enum HeaderFormat {
 	RF64,
 	RF64_WAV,
 	MBWF,
+	FLAC,
 };
 
 struct PeakData {
diff --git a/libs/ardour/enums.cc b/libs/ardour/enums.cc
index 5b7bbe457d..4ff286a1d7 100644
--- a/libs/ardour/enums.cc
+++ b/libs/ardour/enums.cc
@@ -380,6 +380,7 @@ setup_enum_writer ()
 	REGISTER_ENUM (RF64);
 	REGISTER_ENUM (RF64_WAV);
 	REGISTER_ENUM (MBWF);
+	REGISTER_ENUM (FLAC);
 	REGISTER (_HeaderFormat);
 
 	REGISTER_ENUM (AudioUnit);
diff --git a/libs/ardour/luabindings.cc b/libs/ardour/luabindings.cc
index 36c63a9269..899e98a7fe 100644
--- a/libs/ardour/luabindings.cc
+++ b/libs/ardour/luabindings.cc
@@ -1947,6 +1947,7 @@ LuaBindings::common (lua_State* L)
 		.addConst ("RF64", ARDOUR::HeaderFormat(RF64))
 		.addConst ("RF64_WAV", ARDOUR::HeaderFormat(RF64_WAV))
 		.addConst ("MBWF", ARDOUR::HeaderFormat(MBWF))
+		.addConst ("FLAC", ARDOUR::HeaderFormat(FLAC))
 		.endNamespace ()
 
 		.beginNamespace ("InsertMergePolicy")
diff --git a/libs/ardour/sndfilesource.cc b/libs/ardour/sndfilesource.cc
index df228cb69e..ac10f94ae1 100644
--- a/libs/ardour/sndfilesource.cc
+++ b/libs/ardour/sndfilesource.cc
@@ -133,6 +133,15 @@ SndFileSource::SndFileSource (Session& s, const string& path, const string& orig
 		_flags = Flag (_flags & ~Broadcast);
 		break;
 
+	case FLAC:
+		fmt = SF_FORMAT_FLAC;
+		if (sfmt == FormatFloat) {
+			sfmt = FormatInt24;
+		}
+		_flags = Flag (_flags & ~Broadcast);
+		_flags = Flag (_flags & ~Destructive); // XXX or force WAV if destructive?
+		break;
+
 	case AIFF:
 		fmt = SF_FORMAT_AIFF;
 		_flags = Flag (_flags & ~Broadcast);
@@ -384,8 +393,8 @@ SndFileSource::open ()
 	}
 
 	if ((_info.format & SF_FORMAT_TYPEMASK ) == SF_FORMAT_FLAC) {
-		assert (!writable());
-		_sndfile = sf_open_fd (fd, SFM_READ, &_info, true);
+		assert (!destructive());
+		_sndfile = sf_open_fd (fd, writable () ? SFM_WRITE : SFM_READ, &_info, true);
 	} else {
 		_sndfile = sf_open_fd (fd, writable() ? SFM_RDWR : SFM_READ, &_info, true);
 	}
diff --git a/libs/ardour/utils.cc b/libs/ardour/utils.cc
index dd893f399d..96a1b8a2e4 100644
--- a/libs/ardour/utils.cc
+++ b/libs/ardour/utils.cc
@@ -568,6 +568,8 @@ ARDOUR::native_header_format_extension (HeaderFormat hf, const DataType& type)
                 return ".aif";
         case iXML:
                 return ".ixml";
+        case FLAC:
+                return ".flac";
         case RF64:
         case RF64_WAV:
         case MBWF: