A backport of https://github.com/octo/liboping/pull/61
--- a/src/oping.c
+++ b/src/oping.c
@@ -1125,7 +1125,7 @@ static int update_graph_prettyping (ping_context_t *ctx, /* {{{ */
 			wattron (ctx->window, COLOR_PAIR(color));
 
 		if (has_utf8())
-			mvwprintw (ctx->window, /* y = */ 3, /* x = */ x + 2, symbol);
+			mvwprintw (ctx->window, /* y = */ 3, /* x = */ x + 2, "%s", symbol);
 		else
 			mvwaddch (ctx->window, /* y = */ 3, /* x = */ x + 2, symbolc);
 
@@ -1222,7 +1222,7 @@ static int update_graph_histogram (ping_context_t *ctx) /* {{{ */
 		if (counters[x] == 0)
 			mvwaddch (ctx->window, /* y = */ 3, /* x = */ x + 2, ' ');
 		else if (has_utf8 ())
-			mvwprintw (ctx->window, /* y = */ 3, /* x = */ x + 2,
+			mvwprintw (ctx->window, /* y = */ 3, /* x = */ x + 2, "%s",
 					hist_symbols_utf8[index]);
 		else
 			mvwaddch (ctx->window, /* y = */ 3, /* x = */ x + 2,