diff --git a/libtwolame/twolame.h b/libtwolame/twolame.h
index 6b3ee9d..9aaba95 100644
--- a/libtwolame/twolame.h
+++ b/libtwolame/twolame.h
@@ -56,9 +56,9 @@ extern "C" {
 #  endif
 # endif
 #else
-# ifdef GNUC
-#  if GNUC >= 4
-#   define TL_API attribute ((visibility("default")))
+# ifdef __GNUC__
+#  if __GNUC__ >= 4
+#   define TL_API __attribute__ ((visibility("default")))
 #  else
 #   define TL_API
 #  endif
@@ -263,7 +263,7 @@ TL_API int twolame_encode_buffer_float32(twolame_options * glopts,
  *  \return                The number of bytes put in output buffer
  *                         or a negative value on error
  */
-int twolame_encode_buffer_float32_interleaved(twolame_options * glopts,
+TL_API int twolame_encode_buffer_float32_interleaved(twolame_options * glopts,
         const float pcm[],
         int num_samples,
         unsigned char *mp2buffer, int mp2buffer_size);