diff --git a/papers/format.md b/papers/format.md
index b04deac7..d5b9c67e 100644
--- a/papers/format.md
+++ b/papers/format.md
@@ -29,6 +29,7 @@ furthermore, an `or reserved` indicates this field is always present, but is res
 
 the format versions are:
 
+- 66: Furnace dev66
 - 65: Furnace dev65
 - 64: Furnace dev64
 - 63: Furnace dev63
@@ -207,7 +208,8 @@ size | description
   1  | continuous vibrato (>=62) or reserved
   1  | broken DAC mode (>=64) or reserved
   1  | one tick cut (>=65) or reserved
-  2  | reserved
+  1  | instrument change allowed during porta (>=66) or reserved
+  1  | reserved
  4?? | pointers to instruments
  4?? | pointers to wavetables
  4?? | pointers to samples
diff --git a/src/engine/engine.h b/src/engine/engine.h
index fc70c873..b75fc2f0 100644
--- a/src/engine/engine.h
+++ b/src/engine/engine.h
@@ -37,8 +37,8 @@
     warnings+=(String("\n")+x); \
   }
 
-#define DIV_VERSION "dev65"
-#define DIV_ENGINE_VERSION 65
+#define DIV_VERSION "dev66"
+#define DIV_ENGINE_VERSION 66
 
 enum DivStatusView {
   DIV_STATUS_NOTHING=0,
@@ -69,7 +69,7 @@ enum DivHaltPositions {
 
 struct DivChannelState {
   std::vector<DivDelayedCommand> delayed;
-  int note, oldNote, pitch, portaSpeed, portaNote;
+  int note, oldNote, lastIns, pitch, portaSpeed, portaNote;
   int volume, volSpeed, cut, rowDelay, volMax;
   int delayOrder, delayRow, retrigSpeed, retrigTick;
   int vibratoDepth, vibratoRate, vibratoPos, vibratoDir, vibratoFine;
@@ -80,6 +80,7 @@ struct DivChannelState {
   DivChannelState():
     note(-1),
     oldNote(-1),
+    lastIns(-1),
     pitch(0),
     portaSpeed(-1),
     portaNote(-1),
diff --git a/src/engine/fileOps.cpp b/src/engine/fileOps.cpp
index 3c1a9d2a..524531f8 100644
--- a/src/engine/fileOps.cpp
+++ b/src/engine/fileOps.cpp
@@ -142,6 +142,7 @@ bool DivEngine::loadDMF(unsigned char* file, size_t len) {
     ds.ignoreDuplicateSlides=true;
     ds.brokenDACMode=true;
     ds.oneTickCut=false;
+    ds.newInsTriggersInPorta=true;
 
     // 1.1 compat flags
     if (ds.version>24) {
@@ -807,6 +808,9 @@ bool DivEngine::loadFur(unsigned char* file, size_t len) {
     if (ds.version<65) {
       ds.oneTickCut=false;
     }
+    if (ds.version<66) {
+      ds.newInsTriggersInPorta=false;
+    }
     ds.isDMF=false;
 
     reader.readS(); // reserved
@@ -993,7 +997,12 @@ bool DivEngine::loadFur(unsigned char* file, size_t len) {
       } else {
         reader.readC();
       }
-      for (int i=0; i<2; i++) reader.readC();
+      if (ds.version>=66) {
+        ds.newInsTriggersInPorta=reader.readC();
+      } else {
+        reader.readC();
+      }
+      for (int i=0; i<1; i++) reader.readC();
     } else {
       for (int i=0; i<20; i++) reader.readC();
     }
@@ -1437,7 +1446,8 @@ SafeWriter* DivEngine::saveFur() {
   w->writeC(song.continuousVibrato);
   w->writeC(song.brokenDACMode);
   w->writeC(song.oneTickCut);
-  for (int i=0; i<2; i++) {
+  w->writeC(song.newInsTriggersInPorta);
+  for (int i=0; i<1; i++) {
     w->writeC(0);
   }
 
diff --git a/src/engine/playback.cpp b/src/engine/playback.cpp
index 4626635b..8a543fee 100644
--- a/src/engine/playback.cpp
+++ b/src/engine/playback.cpp
@@ -654,6 +654,12 @@ void DivEngine::processRow(int i, bool afterDelay) {
   // instrument
   if (pat->data[whatRow][2]!=-1) {
     dispatchCmd(DivCommand(DIV_CMD_INSTRUMENT,i,pat->data[whatRow][2]));
+    if (chan[i].lastIns!=pat->data[whatRow][2]) {
+      chan[i].lastIns=pat->data[whatRow][2];
+      if (chan[i].inPorta && song.newInsTriggersInPorta) {
+        dispatchCmd(DivCommand(DIV_CMD_NOTE_ON,i,DIV_NOTE_NULL));
+      }
+    }
   }
   // note
   if (pat->data[whatRow][0]==100) { // note off
diff --git a/src/engine/song.h b/src/engine/song.h
index 5747aa51..7fc6ec7f 100644
--- a/src/engine/song.h
+++ b/src/engine/song.h
@@ -297,6 +297,7 @@ struct DivSong {
   bool continuousVibrato;
   bool brokenDACMode;
   bool oneTickCut;
+  bool newInsTriggersInPorta;
 
   DivOrders orders;
   std::vector<DivInstrument*> ins;
@@ -363,7 +364,8 @@ struct DivSong {
     stopPortaOnNoteOff(false),
     continuousVibrato(false),
     brokenDACMode(false),
-    oneTickCut(false) {
+    oneTickCut(false),
+    newInsTriggersInPorta(true) {
     for (int i=0; i<32; i++) {
       system[i]=DIV_SYSTEM_NULL;
       systemVol[i]=64;
diff --git a/src/gui/gui.cpp b/src/gui/gui.cpp
index 3143f684..24b7d46b 100644
--- a/src/gui/gui.cpp
+++ b/src/gui/gui.cpp
@@ -2216,6 +2216,10 @@ void FurnaceGUI::drawCompatFlags() {
     if (ImGui::IsItemHovered()) {
       ImGui::SetTooltip("behavior changed in 0.6");
     }
+    ImGui::Checkbox("Allow instrument change during slides",&e->song.newInsTriggersInPorta);
+    if (ImGui::IsItemHovered()) {
+      ImGui::SetTooltip("behavior changed in 0.6");
+    }
   }
   if (ImGui::IsWindowFocused(ImGuiFocusedFlags_ChildWindows)) curWindow=GUI_WINDOW_COMPAT_FLAGS;
   ImGui::End();