diff --git a/src/gmio_core/error.h b/src/gmio_core/error.h
index d3ab1e5..eba71b7 100644
--- a/src/gmio_core/error.h
+++ b/src/gmio_core/error.h
@@ -29,23 +29,23 @@ enum gmio_error
     GMIO_ERROR_OK = 0,
 
     /*! Pointer on argument gmio_transfer_t is NULL */
-    GMIO_ERROR_NULL_TRANSFER = -1,
+    GMIO_ERROR_NULL_TRANSFER,
 
     /*! Pointer on argument buffer is NULL */
-    GMIO_ERROR_NULL_BUFFER = -2,
+    GMIO_ERROR_NULL_BUFFER,
 
     /*! Argument buffer's size is too small */
-    GMIO_ERROR_INVALID_BUFFER_SIZE = -3,
+    GMIO_ERROR_INVALID_BUFFER_SIZE,
 
     /*! An error occurred with gmio_stream */
-    GMIO_ERROR_STREAM = -4,
+    GMIO_ERROR_STREAM,
 
     /*! Transfer was stopped by user, that is to say
      *  gmio_transfer::is_stop_requested_func() returned GMIO_TRUE */
-    GMIO_ERROR_TRANSFER_STOPPED = -5,
+    GMIO_ERROR_TRANSFER_STOPPED,
 
     /*! Unknown error */
-    GMIO_ERROR_UNKNOWN = -6
+    GMIO_ERROR_UNKNOWN
 };
 
 typedef enum gmio_error gmio_error_t;
diff --git a/src/gmio_stl/stl_error.h b/src/gmio_stl/stl_error.h
index 752134d..053d636 100644
--- a/src/gmio_stl/stl_error.h
+++ b/src/gmio_stl/stl_error.h
@@ -28,34 +28,34 @@ enum { GMIO_STL_ERROR_TAG = 0x11000000 };
 enum gmio_stl_error
 {
     /*! STL format could not be guessed in read function */
-    GMIO_STL_ERROR_UNKNOWN_FORMAT = GMIO_STL_ERROR_TAG + 1,
+    GMIO_STL_ERROR_UNKNOWN_FORMAT = GMIO_STL_ERROR_TAG + 0x01,
 
     /*! Common STL write error indicating gmio_stl_mesh::get_triangle_func()
      *  pointer is NULL
      */
-    GMIO_STL_ERROR_NULL_GET_TRIANGLE_FUNC = GMIO_STL_ERROR_TAG + 2,
+    GMIO_STL_ERROR_NULL_GET_TRIANGLE_FUNC = GMIO_STL_ERROR_TAG + 0x02,
 
     /* Specific error codes returned by STL_ascii read function */
 
     /*! Parsing error occured in gmio_stla_read() due to malformed STL ascii
      *  input */
-    GMIO_STL_ERROR_PARSING = GMIO_STL_ERROR_TAG + 100,
+    GMIO_STL_ERROR_PARSING = GMIO_STL_ERROR_TAG + 0x100,
 
     /*! Invalid max number of decimal significants digits for
      *  gmio_stla_write(), must be in [1..9] */
-    GMIO_STL_ERROR_INVALID_FLOAT32_PREC = GMIO_STL_ERROR_TAG + 101,
+    GMIO_STL_ERROR_INVALID_FLOAT32_PREC = GMIO_STL_ERROR_TAG + 0x101,
 
     /* Specific error codes returned by STL_binary read/write functions */
 
     /*! The byte order argument supplied is not supported, must be little or
      *  big endian */
-    GMIO_STL_ERROR_UNSUPPORTED_BYTE_ORDER = GMIO_STL_ERROR_TAG + 300,
+    GMIO_STL_ERROR_UNSUPPORTED_BYTE_ORDER = GMIO_STL_ERROR_TAG + 0x1000,
 
     /*! Error occured when reading header data in gmio_stlb_read() */
-    GMIO_STL_ERROR_HEADER_WRONG_SIZE = GMIO_STL_ERROR_TAG + 301,
+    GMIO_STL_ERROR_HEADER_WRONG_SIZE = GMIO_STL_ERROR_TAG + 0x1001,
 
     /*! Error occured when reading facet count in gmio_stlb_read() */
-    GMIO_STL_ERROR_FACET_COUNT = GMIO_STL_ERROR_TAG + 302
+    GMIO_STL_ERROR_FACET_COUNT = GMIO_STL_ERROR_TAG + 0x1002
 };
 
 typedef enum gmio_stl_error  gmio_stl_error_t;