diff --git a/dlls/mfplat/main.c b/dlls/mfplat/main.c
index e946bc79f50..f8f4b502a5b 100644
--- a/dlls/mfplat/main.c
+++ b/dlls/mfplat/main.c
@@ -606,7 +606,7 @@ struct guid_def
     const char *name;
 };
 
-static int debug_compare_guid(const void *a, const void *b)
+static int __cdecl debug_compare_guid(const void *a, const void *b)
 {
     const GUID *guid = a;
     const struct guid_def *guid_def = b;
@@ -946,7 +946,7 @@ struct event_id
     const char *name;
 };
 
-static int debug_event_id(const void *a, const void *b)
+static int __cdecl debug_event_id(const void *a, const void *b)
 {
     const DWORD *id = a;
     const struct event_id *event_id = b;
diff --git a/dlls/mfplat/mediatype.c b/dlls/mfplat/mediatype.c
index e23ebd1fb96..aace04fe84e 100644
--- a/dlls/mfplat/mediatype.c
+++ b/dlls/mfplat/mediatype.c
@@ -1735,7 +1735,7 @@ struct uncompressed_video_format
     unsigned int bytes_per_pixel;
 };
 
-static int uncompressed_video_format_compare(const void *a, const void *b)
+static int __cdecl uncompressed_video_format_compare(const void *a, const void *b)
 {
     const GUID *guid = a;
     const struct uncompressed_video_format *format = b;