diff --git a/src/osgPlugins/mdl/MDLReader.h b/src/osgPlugins/mdl/MDLReader.h
index d5c571f9d..84e88e724 100644
--- a/src/osgPlugins/mdl/MDLReader.h
+++ b/src/osgPlugins/mdl/MDLReader.h
@@ -127,9 +127,9 @@ struct MDLHeader
     int           vertex_base;
     int           offset_base;
 
-    u_char        const_direction_light_dot;
-    u_char        root_lod;
-    u_char        unused_byte[2];
+    unsigned char const_direction_light_dot;
+    unsigned char root_lod;
+    unsigned char unused_byte[2];
 
     int           zero_frame_cache_offset;
 
diff --git a/src/osgPlugins/mdl/VVDReader.h b/src/osgPlugins/mdl/VVDReader.h
index f99040b30..25c867c57 100644
--- a/src/osgPlugins/mdl/VVDReader.h
+++ b/src/osgPlugins/mdl/VVDReader.h
@@ -52,9 +52,9 @@ struct VVDFixupEntry
 
 struct VVDBoneWeight
 {
-    float    weight[MAX_BONES_PER_VERTEX];
-    char     bone[MAX_BONES_PER_VERTEX];
-    u_char   num_bones;
+    float           weight[MAX_BONES_PER_VERTEX];
+    char            bone[MAX_BONES_PER_VERTEX];
+    unsigned char   num_bones;
 };