diff --git a/src/osgVolume/Shaders/volume_iso_frag.cpp b/src/osgVolume/Shaders/volume_iso_frag.cpp
index fbfb3c98b..7f0084b87 100644
--- a/src/osgVolume/Shaders/volume_iso_frag.cpp
+++ b/src/osgVolume/Shaders/volume_iso_frag.cpp
@@ -117,7 +117,10 @@ char volume_iso_frag[] = "uniform sampler3D baseTexture;\n"
                          "\n"
                          "            fragColor = vec4(lightScale, lightScale, lightScale, 1.0);\n"
                          "            \n"
-                         "            break;\n"
+                         "            if (fragColor.w>1.0) fragColor.w = 1.0; \n"
+                         "            gl_FragColor = fragColor;\n"
+                         "            \n"
+                         "            return;\n"
                          "        }\n"
                          "        \n"
                          "        previousColor = color;\n"
@@ -127,7 +130,9 @@ char volume_iso_frag[] = "uniform sampler3D baseTexture;\n"
                          "        --num_iterations;\n"
                          "    }\n"
                          "\n"
-                         "    if (fragColor.w>1.0) fragColor.w = 1.0; \n"
-                         "    gl_FragColor = fragColor;\n"
+                         "    // we didn't find an intersection so just discard fragment\n"
+                         "    discard;\n"
+                         "\n"
                          "}\n"
+                         ";\n"
                          "\n";