diff --git a/graphics/pixelformat.cpp b/graphics/pixelformat.cpp
index e7b5401ed66..a712813b45a 100644
--- a/graphics/pixelformat.cpp
+++ b/graphics/pixelformat.cpp
@@ -25,7 +25,7 @@
 
 namespace Graphics {
 
-Common::String PixelFormat::toString() {
+Common::String PixelFormat::toString() const {
 	if (bytesPerPixel == 1)
 		return "CLUT8";
 
diff --git a/graphics/pixelformat.h b/graphics/pixelformat.h
index 3e6c53b05fb..9dd06241b7b 100644
--- a/graphics/pixelformat.h
+++ b/graphics/pixelformat.h
@@ -262,7 +262,7 @@ struct PixelFormat {
 		return 0;
 	}
 
-	Common::String toString();
+	Common::String toString() const;
 };
 
 } // End of namespace Graphics