diff --git a/FL/Fl_Simple_Terminal.H b/FL/Fl_Simple_Terminal.H
index 10ed81bdb..74b012810 100644
--- a/FL/Fl_Simple_Terminal.H
+++ b/FL/Fl_Simple_Terminal.H
@@ -161,7 +161,6 @@ private:
 private:
   int  history_lines_;      // max lines allowed in screen history
   bool stay_at_bottom_;     // lets scroller chase last line in buffer
-  bool ansi_;               // enables ANSI sequences
   // scroll management
   int  lines_;              // #lines in buffer (optimization: Fl_Text_Buffer slow to calc this)
   bool scrollaway_;         // true when user changed vscroll away from bottom
@@ -175,7 +174,10 @@ private:
   int  normal_style_index_;  // "normal" style used by "\033[0m" reset sequence
   int  current_style_index_; // current style used for drawing text
   char current_style_;       // current 'style char' (e.g. 'A' = first style entry)
+  // ANSI escape seq
   Fl_Escape_Seq escseq;      // escape sequence state handler
+  bool ansi_;                // enables ANSI sequences
+  bool ansi_show_unknown_;   // show '¿' for unknown ESC sequences (default: off)
   // String parsing vars initialized/used by append(), used by handle_backspace() etc.
   char *ntm_;                // new text memory  (ntm) - malloc()ed by append() for output text
   char *ntp_;                // new text ptr     (ntp) - points into ntm buffer
@@ -193,6 +195,8 @@ public:
   int  history_lines() const;
   void ansi(bool val);
   bool ansi() const;
+  void ansi_show_unknown(bool val);
+  bool ansi_show_unknown() const;
   void style_table(Fl_Text_Display::Style_Table_Entry *stable, int stable_size, int normal_style_index=0);
   const Fl_Text_Display::Style_Table_Entry *style_table() const;
   int style_table_size() const;
@@ -234,6 +238,7 @@ protected:
   void backspace_buffer(unsigned int count);
   void handle_backspace();
   void append_ansi(const char *s, int len);
+  void unknown_escape();
 };
 
 #endif
diff --git a/src/Fl_Simple_Terminal.cxx b/src/Fl_Simple_Terminal.cxx
index 680b157dd..3f7ade3eb 100644
--- a/src/Fl_Simple_Terminal.cxx
+++ b/src/Fl_Simple_Terminal.cxx
@@ -287,7 +287,6 @@ void Fl_Simple_Terminal::vscroll_cb(Fl_Widget *w, void *data) {
 Fl_Simple_Terminal::Fl_Simple_Terminal(int X,int Y,int W,int H,const char *l) : Fl_Text_Display(X,Y,W,H,l) {
   history_lines_ = 500;         // something 'reasonable'
   stay_at_bottom_ = true;
-  ansi_ = false;
   lines_ = 0;                    // note: lines!=mNBufferLines when lines are wrapping
   scrollaway_ = false;
   scrolling_ = false;
@@ -312,6 +311,9 @@ Fl_Simple_Terminal::Fl_Simple_Terminal(int X,int Y,int W,int H,const char *l) :
   normal_style_index_  = builtin_normal_index;
   current_style_index_ = builtin_normal_index;
   current_style_       = 'A' + 0;
+  // ANSI escape seq
+  ansi_ = false;
+  ansi_show_unknown_ = false;
   // Intercept vertical scrolling
   orig_vscroll_cb_     = mVScrollBar->callback();
   orig_vscroll_data_   = mVScrollBar->user_data();
@@ -470,6 +472,23 @@ void Fl_Simple_Terminal::ansi(bool val) {
   redraw();
 }
 
+/**
+ See if we should show unknown ANSI sequences with '¿' or not.
+ \see ansi_show_unknown(bool)
+*/
+bool Fl_Simple_Terminal::ansi_show_unknown(void) const {
+  return ansi_show_unknown_;
+}
+
+/**
+ Enable showing unknown ESC sequences with the '¿' character.
+ By default this is off, and unknown escape sequences are silently ignored.
+ \see ansi_show_unknown()
+*/
+void Fl_Simple_Terminal::ansi_show_unknown(bool val) {
+  ansi_show_unknown_ = val;
+}
+
 /**
  Return the current style table being used.
 
@@ -760,6 +779,16 @@ void Fl_Simple_Terminal::handle_backspace() {
   backspace_buffer(1);
 } 
 
+// Handle unknown esc sequences
+void Fl_Simple_Terminal::unknown_escape() {
+  if ( ansi_show_unknown() ) {
+    for ( const char *s = "¿"; *s; s++ ) {
+      *ntp_++ = *s;                        // emit utf-8 encoded char
+      *nsp_++ = current_style();           // use current style
+    }
+  }
+}
+
 /**
  Handle appending string with ANSI escape sequences, and other 'special'
  character processing (such as backspaces).
@@ -782,6 +811,7 @@ void Fl_Simple_Terminal::append_ansi(const char *s, int len) {
       if ( escseq.parse_in_progress() ) {   // ESC sequence in progress?
         switch ( escseq.parse(*sp) ) {      // parse until completed or fail
           case Fl_Escape_Seq::fail:         // parsing error?
+            unknown_escape();
             escseq.reset();                 // ..reset and continue
             ++sp;
             continue;
@@ -801,10 +831,10 @@ void Fl_Simple_Terminal::append_ansi(const char *s, int len) {
             case 'J':                       // ESC[#J
               switch (val) {
                 case 0:                     // ESC[0J -- clear to eol
-                  // unsupported
+                  unknown_escape();
                   break;
                 case 1:                     // ESC[1J -- clear to sol
-                  // unsupported
+                  unknown_escape();
                   break;
                 case 2:                     // ESC[2J -- clear visible screen
                   // NOTE: Currently we clear the /entire screen history/, and
@@ -817,6 +847,9 @@ void Fl_Simple_Terminal::append_ansi(const char *s, int len) {
                   ntp_ = ntm_;              // clear text contents accumulated so far
                   nsp_ = nsm_;              // clear style contents ""
                   break;
+                default:                    // all other ESC[#J unsupported
+                  unknown_escape();
+                  break;
               }
               break;
             // SELECT GRAPHIC RENDITION (SGR)
@@ -831,6 +864,7 @@ void Fl_Simple_Terminal::append_ansi(const char *s, int len) {
               break;
             // UNSUPPORTED MODES
             default:
+              unknown_escape();
               break;                         // unsupported
           }
         }