diff --git a/dlls/imaadp32.acm/imaadp32.c b/dlls/imaadp32.acm/imaadp32.c
index 6174c8521f0..9a2fb537c90 100644
--- a/dlls/imaadp32.acm/imaadp32.c
+++ b/dlls/imaadp32.acm/imaadp32.c
@@ -697,8 +697,7 @@ static	LRESULT	ADPCM_FormatSuggest(PACMDRVFORMATSUGGEST adfs)
         if (ADPCM_GetFormatIndex(adfs->pwfxDst) == 0xFFFFFFFF) return ACMERR_NOTPOSSIBLE;
         break;
     default:
-        FIXME("\n");
-        break;
+        return ACMERR_NOTPOSSIBLE;
     }
 
     return MMSYSERR_NOERROR;