diff --git a/ChangeLog b/ChangeLog
index 45567e9bff..3807f6f1ec 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2008-05-19  Tim-Philipp Müller  <tim.muller at collabora co uk>
+
+	* gst/typefind/gsttypefindfunctions.c: (data_scan_ctx_ensure_data),
+	  (mpeg_sys_is_valid_pack):
+	  Don't modify scan context when we return FALSE in ensure_data, so
+	  it's possible to continue scanning, and we don't end up with a NULL
+	  data pointer and a positive size, which might bite us the next time
+	  we're called. Small constification.
+
 2008-05-16  Sebastian Dröge  <slomo@circular-chaos.org>
 
 	* gst/adder/gstadder.c:
diff --git a/common b/common
index 3b3631082d..e365978c48 160000
--- a/common
+++ b/common
@@ -1 +1 @@
-Subproject commit 3b3631082d04b426f450810e8836de94e9c5d60a
+Subproject commit e365978c480a8fffa4bdb61568fb2cd989d1b197
diff --git a/gst/typefind/gsttypefindfunctions.c b/gst/typefind/gsttypefindfunctions.c
index bccaac06e2..d9eae0ecef 100644
--- a/gst/typefind/gsttypefindfunctions.c
+++ b/gst/typefind/gsttypefindfunctions.c
@@ -45,7 +45,7 @@ GST_DEBUG_CATEGORY_STATIC (type_find_debug);
 typedef struct
 {
   guint64 offset;
-  guint8 *data;
+  const guint8 *data;
   gint size;
 } DataScanCtx;
 
@@ -65,13 +65,15 @@ data_scan_ctx_advance (GstTypeFind * tf, DataScanCtx * c, guint bytes_to_skip)
 static inline gboolean
 data_scan_ctx_ensure_data (GstTypeFind * tf, DataScanCtx * c, gint min_len)
 {
+  const guint8 *data;
   guint64 len;
 
   if (G_LIKELY (c->size >= min_len))
     return TRUE;
 
-  c->data = gst_type_find_peek (tf, c->offset, DATA_SCAN_CTX_CHUNK_SIZE);
-  if (G_LIKELY (c->data != NULL)) {
+  data = gst_type_find_peek (tf, c->offset, DATA_SCAN_CTX_CHUNK_SIZE);
+  if (G_LIKELY (data != NULL)) {
+    c->data = data;
     c->size = DATA_SCAN_CTX_CHUNK_SIZE;
     return TRUE;
   }
@@ -86,8 +88,9 @@ data_scan_ctx_ensure_data (GstTypeFind * tf, DataScanCtx * c, gint min_len)
     len = min_len;
   }
 
-  c->data = gst_type_find_peek (tf, c->offset, len);
-  if (c->data != NULL) {
+  data = gst_type_find_peek (tf, c->offset, len);
+  if (data != NULL) {
+    c->data = data;
     c->size = len;
     return TRUE;
   }
@@ -1241,7 +1244,7 @@ static GstStaticCaps mpeg_sys_caps = GST_STATIC_CAPS ("video/mpeg, "
 #define MPEG2_MAX_SYS_HEADERS 5
 
 static gboolean
-mpeg_sys_is_valid_pack (GstTypeFind * tf, guint8 * data, guint len,
+mpeg_sys_is_valid_pack (GstTypeFind * tf, const guint8 * data, guint len,
     guint * pack_size)
 {
   /* Check the pack header @ offset for validity, assuming that the 4 byte header