diff --git a/src/osgPlugins/obj/obj.cpp b/src/osgPlugins/obj/obj.cpp
index 61b788b61..a3f7ec2bc 100644
--- a/src/osgPlugins/obj/obj.cpp
+++ b/src/osgPlugins/obj/obj.cpp
@@ -425,9 +425,9 @@ bool Model::readMTL(std::istream& fin)
                 {
                     material->map_Ks = parseTexture(strip(line+7), *material);
                 }
-                else if (strncmp(line,"map_opacity ",7)==0)
+                else if (strncmp(line,"map_opacity ",12)==0)
                 {
-                    material->map_opacity = parseTexture(strip(line+7), *material);
+                    material->map_opacity = parseTexture(strip(line+12), *material);
                 }
                 else if (strcmp(line,"refl")==0 || strncmp(line,"refl ",5)==0)
                 {