diff --git a/dlls/msacm32/format.c b/dlls/msacm32/format.c
index f7f0fa40ac3..1ab05ae2136 100644
--- a/dlls/msacm32/format.c
+++ b/dlls/msacm32/format.c
@@ -676,6 +676,9 @@ MMRESULT WINAPI acmFormatSuggest(HACMDRIVER had, PWAVEFORMATEX pwfxSrc,
     TRACE("(%p, %p, %p, %d, %d)\n",
 	  had, pwfxSrc, pwfxDst, cbwfxDst, fdwSuggest);
 
+    if (!pwfxSrc || !pwfxDst)
+        return MMSYSERR_INVALPARAM;
+
     if (fdwSuggest & ~(ACM_FORMATSUGGESTF_NCHANNELS|ACM_FORMATSUGGESTF_NSAMPLESPERSEC|
 		       ACM_FORMATSUGGESTF_WBITSPERSAMPLE|ACM_FORMATSUGGESTF_WFORMATTAG))
 	return MMSYSERR_INVALFLAG;