diff --git a/dlls/mf/mf_private.h b/dlls/mf/mf_private.h
index db6f101cd6d..6f28c93aea3 100644
--- a/dlls/mf/mf_private.h
+++ b/dlls/mf/mf_private.h
@@ -79,6 +79,40 @@ static inline const char *debugstr_time(LONGLONG time)
     return wine_dbg_sprintf("%s", rev);
 }
 
+static inline const char *debugstr_propvar(const PROPVARIANT *v)
+{
+    if (!v)
+        return "(null)";
+
+    switch (v->vt)
+    {
+        case VT_EMPTY:
+            return wine_dbg_sprintf("%p {VT_EMPTY}", v);
+        case VT_NULL:
+            return wine_dbg_sprintf("%p {VT_NULL}", v);
+        case VT_UI4:
+            return wine_dbg_sprintf("%p {VT_UI4: %ld}", v, v->ulVal);
+        case VT_UI8:
+            return wine_dbg_sprintf("%p {VT_UI8: %s}", v, wine_dbgstr_longlong(v->uhVal.QuadPart));
+        case VT_I8:
+            return wine_dbg_sprintf("%p {VT_I8: %s}", v, wine_dbgstr_longlong(v->hVal.QuadPart));
+        case VT_R4:
+            return wine_dbg_sprintf("%p {VT_R4: %.8e}", v, v->fltVal);
+        case VT_R8:
+            return wine_dbg_sprintf("%p {VT_R8: %lf}", v, v->dblVal);
+        case VT_CLSID:
+            return wine_dbg_sprintf("%p {VT_CLSID: %s}", v, wine_dbgstr_guid(v->puuid));
+        case VT_LPWSTR:
+            return wine_dbg_sprintf("%p {VT_LPWSTR: %s}", v, wine_dbgstr_w(v->pwszVal));
+        case VT_VECTOR | VT_UI1:
+            return wine_dbg_sprintf("%p {VT_VECTOR|VT_UI1: %p}", v, v->caub.pElems);
+        case VT_UNKNOWN:
+            return wine_dbg_sprintf("%p {VT_UNKNOWN: %p}", v, v->punkVal);
+        default:
+            return wine_dbg_sprintf("%p {vt %#x}", v, v->vt);
+    }
+}
+
 extern BOOL mf_is_sample_copier_transform(IMFTransform *transform) DECLSPEC_HIDDEN;
 extern BOOL mf_is_sar_sink(IMFMediaSink *sink) DECLSPEC_HIDDEN;
 extern HRESULT topology_node_get_object(IMFTopologyNode *node, REFIID riid, void **obj) DECLSPEC_HIDDEN;
diff --git a/dlls/mf/session.c b/dlls/mf/session.c
index 29dae316ce0..85cbcc29630 100644
--- a/dlls/mf/session.c
+++ b/dlls/mf/session.c
@@ -2009,7 +2009,7 @@ static HRESULT WINAPI mfsession_Start(IMFMediaSession *iface, const GUID *format
     struct session_op *op;
     HRESULT hr;
 
-    TRACE("%p, %s, %p.\n", iface, debugstr_guid(format), start_position);
+    TRACE("%p, %s, %p.\n", iface, debugstr_guid(format), debugstr_propvar(start_position));
 
     if (!start_position)
         return E_POINTER;