diff --git a/src/audio/SDL_audio.c b/src/audio/SDL_audio.c
index 0aae01549..02deffd4e 100644
--- a/src/audio/SDL_audio.c
+++ b/src/audio/SDL_audio.c
@@ -532,7 +532,7 @@ int SDL_OpenAudio(SDL_AudioSpec *desired, SDL_AudioSpec *obtained)
 			return(-1);
 		}
 		if ( audio->convert.needed ) {
-			audio->convert.len = (int) ( ((double) desired->size) /
+			audio->convert.len = (int) ( ((double) audio->spec.size) /
                                           audio->convert.len_ratio );
 			audio->convert.buf =(Uint8 *)SDL_AllocAudioMem(
 			   audio->convert.len*audio->convert.len_mult);