diff --git a/devel/schemata b/devel/schemata
index cdd0e433..41dc4a60 100644
--- a/devel/schemata
+++ b/devel/schemata
@@ -14,7 +14,17 @@ are interleaved. Keys are printed as keywords (symbols preceded by a
 colon), e.g. (:id "123" :time 54321 :from "foobar"). Null is printed as
 nil, true as t and false as nil.
 
-This is version 1 of the structured output format.
+This is version 2 of the structured output format.
+
+Version history
+---------------
+
+v1
+- First versioned schema release.
+- Added part.content-length and part.content-transfer-encoding fields.
+
+v2
+- Added the thread_summary.query field.
 
 Common non-terminals
 --------------------
@@ -145,7 +155,15 @@ thread_summary = {
     authors:        string,   # comma-separated names with | between
                               # matched and unmatched
     subject:        string,
-    tags:           [string*]
+    tags:           [string*],
+
+    # Two stable query strings identifying exactly the matched and
+    # unmatched messages currently in this thread.  The messages
+    # matched by these queries will not change even if more messages
+    # arrive in the thread.  If there are no matched or unmatched
+    # messages, the corresponding query will be null (there is no
+    # query that matches nothing).  (Added in schema version 2.)
+    query:          [string|null, string|null],
 }
 
 notmuch reply schema
diff --git a/notmuch-client.h b/notmuch-client.h
index 4ecb3ae9..278b498a 100644
--- a/notmuch-client.h
+++ b/notmuch-client.h
@@ -138,7 +138,7 @@ chomp_newline (char *str)
  * this.  New (required) map fields can be added without increasing
  * this.
  */
-#define NOTMUCH_FORMAT_CUR 1
+#define NOTMUCH_FORMAT_CUR 2
 /* The minimum supported structured output format version.  Requests
  * for format versions below this will return an error. */
 #define NOTMUCH_FORMAT_MIN 1
diff --git a/notmuch-search.c b/notmuch-search.c
index d9d39ec3..7c973b3d 100644
--- a/notmuch-search.c
+++ b/notmuch-search.c
@@ -20,6 +20,7 @@
 
 #include "notmuch-client.h"
 #include "sprinter.h"
+#include "string-util.h"
 
 typedef enum {
     OUTPUT_SUMMARY,
@@ -46,6 +47,45 @@ sanitize_string (const void *ctx, const char *str)
     return out;
 }
 
+/* Return two stable query strings that identify exactly the matched
+ * and unmatched messages currently in thread.  If there are no
+ * matched or unmatched messages, the returned buffers will be
+ * NULL. */
+static int
+get_thread_query (notmuch_thread_t *thread,
+		  char **matched_out, char **unmatched_out)
+{
+    notmuch_messages_t *messages;
+    char *escaped = NULL;
+    size_t escaped_len = 0;
+
+    *matched_out = *unmatched_out = NULL;
+
+    for (messages = notmuch_thread_get_messages (thread);
+	 notmuch_messages_valid (messages);
+	 notmuch_messages_move_to_next (messages))
+    {
+	notmuch_message_t *message = notmuch_messages_get (messages);
+	const char *mid = notmuch_message_get_message_id (message);
+	/* Determine which query buffer to extend */
+	char **buf = notmuch_message_get_flag (
+	    message, NOTMUCH_MESSAGE_FLAG_MATCH) ? matched_out : unmatched_out;
+	/* Add this message's id: query.  Since "id" is an exclusive
+	 * prefix, it is implicitly 'or'd together, so we only need to
+	 * join queries with a space. */
+	if (make_boolean_term (thread, "id", mid, &escaped, &escaped_len) < 0)
+	    return -1;
+	if (*buf)
+	    *buf = talloc_asprintf_append_buffer (*buf, " %s", escaped);
+	else
+	    *buf = talloc_strdup (thread, escaped);
+	if (!*buf)
+	    return -1;
+    }
+    talloc_free (escaped);
+    return 0;
+}
+
 static int
 do_search_threads (sprinter_t *format,
 		   notmuch_query_t *query,
@@ -131,6 +171,25 @@ do_search_threads (sprinter_t *format,
 		format->string (format, authors);
 		format->map_key (format, "subject");
 		format->string (format, subject);
+		if (notmuch_format_version >= 2) {
+		    char *matched_query, *unmatched_query;
+		    if (get_thread_query (thread, &matched_query,
+					  &unmatched_query) < 0) {
+			fprintf (stderr, "Out of memory\n");
+			return 1;
+		    }
+		    format->map_key (format, "query");
+		    format->begin_list (format);
+		    if (matched_query)
+			format->string (format, matched_query);
+		    else
+			format->null (format);
+		    if (unmatched_query)
+			format->string (format, unmatched_query);
+		    else
+			format->null (format);
+		    format->end (format);
+		}
 	    }
 
 	    talloc_free (ctx_quote);
diff --git a/test/json b/test/json
index b87b7f6d..e07a2904 100755
--- a/test/json
+++ b/test/json
@@ -26,6 +26,7 @@ test_expect_equal_json "$output" "[{\"thread\": \"XXX\",
  \"total\": 1,
  \"authors\": \"Notmuch Test Suite\",
  \"subject\": \"json-search-subject\",
+ \"query\": [\"id:$gen_msg_id\", null],
  \"tags\": [\"inbox\",
  \"unread\"]}]"
 
@@ -59,6 +60,7 @@ test_expect_equal_json "$output" "[{\"thread\": \"XXX\",
  \"total\": 1,
  \"authors\": \"Notmuch Test Suite\",
  \"subject\": \"json-search-utf8-body-sübjéct\",
+ \"query\": [\"id:$gen_msg_id\", null],
  \"tags\": [\"inbox\",
  \"unread\"]}]"
 
diff --git a/test/missing-headers b/test/missing-headers
index f14b8784..43e861bc 100755
--- a/test/missing-headers
+++ b/test/missing-headers
@@ -43,7 +43,8 @@ test_expect_equal_json "$output" '
         ],
         "thread": "XXX",
         "timestamp": 978709437,
-        "total": 1
+        "total": 1,
+        "query": ["id:notmuch-sha1-7a6e4eac383ef958fcd3ebf2143db71b8ff01161", null]
     },
     {
         "authors": "Notmuch Test Suite",
@@ -56,7 +57,8 @@ test_expect_equal_json "$output" '
         ],
         "thread": "XXX",
         "timestamp": 0,
-        "total": 1
+        "total": 1,
+        "query": ["id:notmuch-sha1-ca55943aff7a72baf2ab21fa74fab3d632401334", null]
     }
 ]'
 
diff --git a/test/sexp b/test/sexp
index 492a82f7..be815e12 100755
--- a/test/sexp
+++ b/test/sexp
@@ -19,7 +19,7 @@ test_expect_equal "$output" "((((:id \"${gen_msg_id}\" :match t :excluded nil :f
 test_begin_subtest "Search message: sexp"
 add_message "[subject]=\"sexp-search-subject\"" "[date]=\"Sat, 01 Jan 2000 12:00:00 -0000\"" "[body]=\"sexp-search-message\""
 output=$(notmuch search --format=sexp "sexp-search-message" | notmuch_search_sanitize)
-test_expect_equal "$output" "((:thread \"0000000000000002\" :timestamp 946728000 :date_relative \"2000-01-01\" :matched 1 :total 1 :authors \"Notmuch Test Suite\" :subject \"sexp-search-subject\" :tags (\"inbox\" \"unread\")))"
+test_expect_equal "$output" "((:thread \"0000000000000002\" :timestamp 946728000 :date_relative \"2000-01-01\" :matched 1 :total 1 :authors \"Notmuch Test Suite\" :subject \"sexp-search-subject\" :query (\"id:$gen_msg_id\" nil) :tags (\"inbox\" \"unread\")))"
 
 test_begin_subtest "Show message: sexp, utf-8"
 add_message "[subject]=\"sexp-show-utf8-body-sübjéct\"" "[date]=\"Sat, 01 Jan 2000 12:00:00 -0000\"" "[body]=\"jsön-show-méssage\""
@@ -44,7 +44,7 @@ test_expect_equal "$output" "((((:id \"$id\" :match t :excluded nil :filename \"
 test_begin_subtest "Search message: sexp, utf-8"
 add_message "[subject]=\"sexp-search-utf8-body-sübjéct\"" "[date]=\"Sat, 01 Jan 2000 12:00:00 -0000\"" "[body]=\"jsön-search-méssage\""
 output=$(notmuch search --format=sexp "jsön-search-méssage" | notmuch_search_sanitize)
-test_expect_equal "$output" "((:thread \"0000000000000005\" :timestamp 946728000 :date_relative \"2000-01-01\" :matched 1 :total 1 :authors \"Notmuch Test Suite\" :subject \"sexp-search-utf8-body-sübjéct\" :tags (\"inbox\" \"unread\")))"
+test_expect_equal "$output" "((:thread \"0000000000000005\" :timestamp 946728000 :date_relative \"2000-01-01\" :matched 1 :total 1 :authors \"Notmuch Test Suite\" :subject \"sexp-search-utf8-body-sübjéct\" :query (\"id:$gen_msg_id\" nil) :tags (\"inbox\" \"unread\")))"
 
 
 test_done