diff --git a/ext/gd/libgd/gd.h b/ext/gd/libgd/gd.h
index 783b3fa403a7a..7e9b619f11014 100644
--- a/ext/gd/libgd/gd.h
+++ b/ext/gd/libgd/gd.h
@@ -878,6 +878,7 @@ gdImagePtr gdImageCropAuto(gdImagePtr im, const unsigned int mode);
 gdImagePtr gdImageCropThreshold(gdImagePtr im, const unsigned int color, const float threshold);
 
 int gdImageSetInterpolationMethod(gdImagePtr im, gdInterpolationMethod id);
+gdInterpolationMethod gdImageGetInterpolationMethod(gdImagePtr im);
 
 gdImagePtr gdImageScaleBilinear(gdImagePtr im, const unsigned int new_width, const unsigned int new_height);
 gdImagePtr gdImageScaleBicubic(gdImagePtr src_img, const unsigned int new_width, const unsigned int new_height);