diff --git a/dlls/avifil32/extrachunk.c b/dlls/avifil32/extrachunk.c
index ac3a04d5748..8fad124220c 100644
--- a/dlls/avifil32/extrachunk.c
+++ b/dlls/avifil32/extrachunk.c
@@ -29,8 +29,7 @@
 WINE_DEFAULT_DEBUG_CHANNEL(avifile);
 
 /* reads a chunk outof the extrachunk-structure */
-HRESULT ReadExtraChunk(LPEXTRACHUNKS extra,FOURCC ckid,LPVOID lpData,
-		       LPLONG size)
+HRESULT ReadExtraChunk(const LPEXTRACHUNKS extra,FOURCC ckid,LPVOID lpData,LPLONG size)
 {
   LPBYTE lp;
   DWORD  cb;
@@ -68,8 +67,7 @@ HRESULT ReadExtraChunk(LPEXTRACHUNKS extra,FOURCC ckid,LPVOID lpData,
 }
 
 /* writes a chunk into the extrachunk-structure */
-HRESULT WriteExtraChunk(LPEXTRACHUNKS extra,FOURCC ckid,LPVOID lpData,
-			LONG size)
+HRESULT WriteExtraChunk(LPEXTRACHUNKS extra,FOURCC ckid,LPCVOID lpData, LONG size)
 {
   LPDWORD lp;
 
diff --git a/dlls/avifil32/extrachunk.h b/dlls/avifil32/extrachunk.h
index b30e9d82c31..981f68e5f5a 100644
--- a/dlls/avifil32/extrachunk.h
+++ b/dlls/avifil32/extrachunk.h
@@ -35,10 +35,10 @@ typedef struct _EXTRACHUNKS {
 } EXTRACHUNKS, *LPEXTRACHUNKS;
 
 /* reads a chunk outof the extrachunk-structure */
-HRESULT ReadExtraChunk(LPEXTRACHUNKS extra,FOURCC ckid,LPVOID lp,LPLONG size);
+HRESULT ReadExtraChunk(const LPEXTRACHUNKS extra,FOURCC ckid,LPVOID lp,LPLONG size);
 
 /* writes a chunk into the extrachunk-structure */
-HRESULT WriteExtraChunk(LPEXTRACHUNKS extra,FOURCC ckid,LPVOID lp,LONG size);
+HRESULT WriteExtraChunk(LPEXTRACHUNKS extra,FOURCC ckid,LPCVOID lp,LONG size);
 
 /* reads a chunk fomr the HMMIO into the extrachunk-structure */
 HRESULT ReadChunkIntoExtra(LPEXTRACHUNKS extra,HMMIO hmmio,MMCKINFO *lpck);