diff --git a/dlls/twain_32/twain32_main.c b/dlls/twain_32/twain32_main.c
index b7db5d2b530..c04e9cf8456 100644
--- a/dlls/twain_32/twain32_main.c
+++ b/dlls/twain_32/twain32_main.c
@@ -33,7 +33,7 @@ WINE_DEFAULT_DEBUG_CHANNEL(twain);
 
 /* A helper function that looks up a destination identity in the active
    source list */
-static activeDS *TWAIN_LookupSource (pTW_IDENTITY pDest)
+static activeDS *TWAIN_LookupSource (const TW_IDENTITY *pDest)
 {
     activeDS *pSource;