https://github.com/vim-jp/issues/issues/1093

syntax.c.diff

diff --git a/src/syntax.c b/src/syntax.c
index e0736cb63..87d374955 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -7354,6 +7354,19 @@ lookup_color(int idx, int foreground, int *boldp)
     return color;
 }
 
+    static void
+update_str_arg(char_u **str, char_u *arg)
+{
+    if (*str == NULL || STRCMP(*str, arg) != 0)
+    {
+	char_u *p = *str;
+
+	/* Avoid allocating same address as freed. */
+	*str = arg != NULL ? vim_strsave(arg) : NULL;
+	vim_free(p);
+    }
+}
+
 /*
  * Handle the ":highlight .." command.
  * When using ":hi clear" this is called recursively for each group with
@@ -7785,8 +7798,7 @@ do_highlight(
 	    else if (!gui.shell_created)
 	    {
 		/* GUI not started yet, always accept the name. */
-		vim_free(HL_TABLE()[idx].sg_font_name);
-		HL_TABLE()[idx].sg_font_name = vim_strsave(arg);
+		update_str_arg(&HL_TABLE()[idx].sg_font_name, arg);
 	    }
 	    else
 	    {
@@ -7813,8 +7825,7 @@ do_highlight(
 		    /* New fontset was accepted. Free the old one, if there
 		     * was one. */
 		    gui_mch_free_fontset(temp_sg_fontset);
-		    vim_free(HL_TABLE()[idx].sg_font_name);
-		    HL_TABLE()[idx].sg_font_name = vim_strsave(arg);
+		    update_str_arg(&HL_TABLE()[idx].sg_font_name, arg);
 		}
 		else
 		    HL_TABLE()[idx].sg_fontset = temp_sg_fontset;
@@ -7824,8 +7835,7 @@ do_highlight(
 		    /* New font was accepted. Free the old one, if there was
 		     * one. */
 		    gui_mch_free_font(temp_sg_font);
-		    vim_free(HL_TABLE()[idx].sg_font_name);
-		    HL_TABLE()[idx].sg_font_name = vim_strsave(arg);
+		    update_str_arg(&HL_TABLE()[idx].sg_font_name, arg);
 		}
 		else
 		    HL_TABLE()[idx].sg_font = temp_sg_font;
@@ -7982,11 +7992,8 @@ do_highlight(
 		{
 		    HL_TABLE()[idx].sg_gui_fg = i;
 # endif
-		    vim_free(HL_TABLE()[idx].sg_gui_fg_name);
-		    if (STRCMP(arg, "NONE") != 0)
-			HL_TABLE()[idx].sg_gui_fg_name = vim_strsave(arg);
-		    else
-			HL_TABLE()[idx].sg_gui_fg_name = NULL;
+		    update_str_arg(&HL_TABLE()[idx].sg_gui_fg_name,
+					STRCMP(arg, "NONE") != 0 ? arg : NULL);
 # if defined(FEAT_GUI) || defined(FEAT_TERMGUICOLORS)
 #  ifdef FEAT_GUI_X11
 		    if (is_menu_group)
@@ -8019,11 +8026,8 @@ do_highlight(
 		{
 		    HL_TABLE()[idx].sg_gui_bg = i;
 # endif
-		    vim_free(HL_TABLE()[idx].sg_gui_bg_name);
-		    if (STRCMP(arg, "NONE") != 0)
-			HL_TABLE()[idx].sg_gui_bg_name = vim_strsave(arg);
-		    else
-			HL_TABLE()[idx].sg_gui_bg_name = NULL;
+		    update_str_arg(&HL_TABLE()[idx].sg_gui_bg_name,
+					STRCMP(arg, "NONE") != 0 ? arg : NULL);
 # if defined(FEAT_GUI) || defined(FEAT_TERMGUICOLORS)
 #  ifdef FEAT_GUI_X11
 		    if (is_menu_group)
@@ -8055,11 +8059,8 @@ do_highlight(
 		{
 		    HL_TABLE()[idx].sg_gui_sp = i;
 # endif
-		    vim_free(HL_TABLE()[idx].sg_gui_sp_name);
-		    if (STRCMP(arg, "NONE") != 0)
-			HL_TABLE()[idx].sg_gui_sp_name = vim_strsave(arg);
-		    else
-			HL_TABLE()[idx].sg_gui_sp_name = NULL;
+		    update_str_arg(&HL_TABLE()[idx].sg_gui_sp_name,
+					STRCMP(arg, "NONE") != 0 ? arg : NULL);
 # ifdef FEAT_GUI
 		}
 # endif
@@ -8136,17 +8137,11 @@ do_highlight(
 	    if (STRCMP(buf, "NONE") == 0)	/* resetting the value */
 		p = NULL;
 	    else
-		p = vim_strsave(buf);
+		p = buf;
 	    if (key[2] == 'A')
-	    {
-		vim_free(HL_TABLE()[idx].sg_start);
-		HL_TABLE()[idx].sg_start = p;
-	    }
+		update_str_arg(&HL_TABLE()[idx].sg_start, p);
 	    else
-	    {
-		vim_free(HL_TABLE()[idx].sg_stop);
-		HL_TABLE()[idx].sg_stop = p;
-	    }
+		update_str_arg(&HL_TABLE()[idx].sg_stop, p);
 	}
 	else
 	{
@@ -8495,10 +8490,7 @@ hl_set_font_name(char_u *font_name)
 
     id = syn_name2id((char_u *)"Normal");
     if (id > 0)
-    {
-	vim_free(HL_TABLE()[id - 1].sg_font_name);
-	HL_TABLE()[id - 1].sg_font_name = vim_strsave(font_name);
-    }
+	update_str_arg(&HL_TABLE()[id - 1].sg_font_name, font_name);
 }
 
 /*