diff --git a/src/graphics/OpenGLDrawMethods.inl b/src/graphics/OpenGLDrawMethods.inl
index 74039f33f..618ca3e5a 100644
--- a/src/graphics/OpenGLDrawMethods.inl
+++ b/src/graphics/OpenGLDrawMethods.inl
@@ -1,5 +1,6 @@
 #include "../data/font.h"
 #include <cmath>
+#include <cstring>
 
 int PIXELMETHODS_CLASS::drawtext_outline(int x, int y, String s, int r, int g, int b, int a)
 {
@@ -15,15 +16,15 @@ int PIXELMETHODS_CLASS::drawtext_outline(int x, int y, String s, int r, int g, i
 int PIXELMETHODS_CLASS::drawtext(int x, int y, String str, int r, int g, int b, int a)
 {
 	bool invert = false;
-	if(!strlen(s))
+	if(str.size() == 0)
 		return 0;
 	int oR = r, oG = g, oB = b;
 	int width, height;
-	Graphics::textsize(s, width, height);
+	Graphics::textsize(str, width, height);
 	VideoBuffer texture(width, height);
 	int characterX = 0, characterY = 0;
 	int startX = characterX;
-	String::value_type *s = str.c_str();
+	const String::value_type *s = str.c_str();
 	for (; *s; s++)
 	{
 		if (*s == '\n')
@@ -131,7 +132,7 @@ int PIXELMETHODS_CLASS::drawtext(int x, int y, String str, int r, int g, int b,
 
 int PIXELMETHODS_CLASS::drawchar(int x, int y, String::value_type c, int r, int g, int b, int a)
 {
-	unsigned char *rp = font_data + font_ptrs[c];
+	const unsigned char *rp = font_data + font_ptrs[c];
 	int w = *(rp++);
 	VideoBuffer texture(w, FONT_H);
 	texture.SetCharacter(0, 0, c, r, g, b, a);
@@ -160,7 +161,7 @@ int PIXELMETHODS_CLASS::drawchar(int x, int y, String::value_type c, int r, int
 
 int PIXELMETHODS_CLASS::addchar(int x, int y, String::value_type c, int r, int g, int b, int a)
 {
-	unsigned char *rp = font_data + font_ptrs[c];
+	const unsigned char *rp = font_data + font_ptrs[c];
 	int w = *(rp++);
 	VideoBuffer texture(w, FONT_H);
 	texture.AddCharacter(0, 0, c, r, g, b, a);