--- a/libinterp/corefcn/__magick_read__.cc	2018-05-22 12:25:37.688173855 +0200
+++ a/libinterp/corefcn/__magick_read__.cc.new	2018-05-22 12:32:51.475172200 +0200
@@ -817,10 +817,11 @@
       // depth is 8, there's a good chance that we will be limited.  It
       // is also the GraphicsMagick recommended setting and the default
       // for ImageMagick.
-      if (QuantumDepth < 16)
+      using namespace Magick;
+      if (MAGICKCORE_QUANTUM_DEPTH < 16)
         warning_with_id ("Octave:GraphicsMagick-Quantum-Depth",
                          "your version of %s limits images to %d bits per pixel\n",
-                         MagickPackageName, QuantumDepth);
+                         MagickPackageName, MAGICKCORE_QUANTUM_DEPTH);
 
       initialized = true;
     }