diff --git a/FL/Fl_Text_Display.H b/FL/Fl_Text_Display.H
index 21f0d63d8..7bc254723 100644
--- a/FL/Fl_Text_Display.H
+++ b/FL/Fl_Text_Display.H
@@ -431,7 +431,8 @@ public:
   int wrapped_row(int row) const;
   void wrap_mode(int wrap, int wrap_margin);
 
-  virtual void recalc_display();
+  virtual void recalc_display();        // does actual recalc
+  virtual void needs_recalc_display();  // schedules recalc during draw()
   virtual void resize(int X, int Y, int W, int H);
 
   /**
@@ -654,6 +655,9 @@ protected:
   Fl_Color    linenumber_bgcolor_;
   Fl_Align    linenumber_align_;
   const char* linenumber_format_;
+
+protected:
+  bool needs_recalc_display_;
 };
 
 #endif
diff --git a/src/Fl_Text_Display.cxx b/src/Fl_Text_Display.cxx
index 1f02c34f5..9a277e060 100644
--- a/src/Fl_Text_Display.cxx
+++ b/src/Fl_Text_Display.cxx
@@ -169,6 +169,7 @@ Fl_Text_Display::Fl_Text_Display(int X, int Y, int W, int H, const char* l)
   secondary_selection_color_ = FL_GRAY;
   mLineNumLeft = 0;             // XXX: UNUSED
   mLineNumWidth = 0;
+  needs_recalc_display_ = false;
 
   linenumber_font_    = FL_HELVETICA;
   linenumber_size_    = FL_NORMAL_SIZE;
@@ -223,7 +224,7 @@ Fl_Text_Display::~Fl_Text_Display() {
 void Fl_Text_Display::linenumber_width(int width) {
   if (width < 0) return;
   mLineNumWidth = width;
-  recalc_display();             // recalc line#s        // resize(x(), y(), w(), h());
+  needs_recalc_display();       // recalc line#s        // resize(x(), y(), w(), h());
 }
 
 /**
@@ -376,7 +377,7 @@ void Fl_Text_Display::buffer( Fl_Text_Buffer *buf ) {
   }
 
   /* Resize the widget to update the screen... */
-  recalc_display();             // resize(x(), y(), w(), h());
+  needs_recalc_display();       // resize(x(), y(), w(), h());
 }
 
 
@@ -478,11 +479,22 @@ void Fl_Text_Display::resize(int X, int Y, int W, int H) {
 
   Fl_Widget::resize(X,Y,W,H);
   mColumnScale = 0; // force recomputation of the width of a column when display is rescaled
-  recalc_display();
+  needs_recalc_display();
+}
+
+/**
+ Schedule a recalc_display() to be done on next draw().
+ Call this from methods that might be called repeatedly, to defers potentially
+ cpu intensive recalc_display() until it's actually needed just before draw().
+ */
+void Fl_Text_Display::needs_recalc_display() {
+  needs_recalc_display_ = true;
 }
 
 /**
  Recalculate the display's visible lines and scrollbar sizes.
+ Beware calling this directly may cause a lot of CPU if called repeatedly (issue 300).
+ Better to call needs_recalc_display() to flag a recalc to be done during next draw().
  */
 void Fl_Text_Display::recalc_display() {
   if (!buffer()) return;
@@ -969,7 +981,7 @@ void Fl_Text_Display::wrap_mode(int wrap, int wrapMargin) {
     mAbsTopLineNum = 1;         // changed from 0 to 1 -- LZA / STR#2621
   }
 
-  recalc_display();             // resize(x(), y(), w(), h());
+  needs_recalc_display();       // resize(x(), y(), w(), h());
 }
 
 
@@ -1278,7 +1290,7 @@ void Fl_Text_Display::display_insert() {
  */
 void Fl_Text_Display::show_insert_position() {
   display_insert_position_hint = 1;
-  recalc_display();             // resize(x(), y(), w(), h());
+  needs_recalc_display();       // resize(x(), y(), w(), h());
 }
 
 
@@ -1746,7 +1758,7 @@ void Fl_Text_Display::buffer_modified_cb( int pos, int nInserted, int nDeleted,
   }
 
   // refigure scrollbars & stuff
-  textD->resize(textD->x(), textD->y(), textD->w(), textD->h());
+  textD->needs_recalc_display(); // textD->resize(textD->x(), textD->y(), textD->w(), textD->h());
 
   // don't need to do anything else if not visible?
   if (!textD->visible_r()) return;
@@ -3004,7 +3016,7 @@ void Fl_Text_Display::calc_last_char() {
 void Fl_Text_Display::scroll(int topLineNum, int horizOffset) {
   mTopLineNumHint = topLineNum;
   mHorizOffsetHint = horizOffset;
-  recalc_display();     // resize(x(), y(), w(), h());
+  needs_recalc_display();     // resize(x(), y(), w(), h());
 }
 
 
@@ -3836,6 +3848,13 @@ void Fl_Text_Display::extend_range_for_styles( int *startpos, int *endpos ) {
  This function tries to limit drawing to smaller areas if possible.
  */
 void Fl_Text_Display::draw(void) {
+
+  // recalc if needed -- issue #300
+  if (needs_recalc_display_) {
+    needs_recalc_display_ = false;
+    recalc_display();
+  }
+
   // don't even try if there is no associated text buffer!
   if (!buffer()) { draw_box(); return; }
 
@@ -3846,7 +3865,7 @@ void Fl_Text_Display::draw(void) {
 
   // draw the non-text, non-scrollbar areas.
   if (damage() & FL_DAMAGE_ALL) {
-    recalc_display();
+    needs_recalc_display();
     //    printf("drawing all (box = %d)\n", box());
     if (Fl_Surface_Device::surface() != Fl_Display_Device::display_device()) {
       // if to printer, draw the background