diff --git a/lib/Makefile.local b/lib/Makefile.local
index 6d67a2a4..4e766305 100644
--- a/lib/Makefile.local
+++ b/lib/Makefile.local
@@ -65,7 +65,8 @@ libnotmuch_cxx_srcs =		\
 	$(dir)/open.cc		\
 	$(dir)/init.cc		\
 	$(dir)/parse-sexp.cc	\
-	$(dir)/sexp-fp.cc
+	$(dir)/sexp-fp.cc	\
+	$(dir)/lastmod-fp.cc
 
 libnotmuch_modules := $(libnotmuch_c_srcs:.c=.o) $(libnotmuch_cxx_srcs:.cc=.o)
 
diff --git a/lib/database-private.h b/lib/database-private.h
index 419b9fe6..b9be4e22 100644
--- a/lib/database-private.h
+++ b/lib/database-private.h
@@ -381,5 +381,11 @@ _notmuch_sexp_string_to_xapian_query (notmuch_database_t *notmuch, const char *q
 notmuch_status_t
 _notmuch_date_strings_to_query (Xapian::valueno slot, const std::string &from, const std::string &to,
 				Xapian::Query &output, std::string &msg);
+
+/* lastmod-fp.h */
+notmuch_status_t
+_notmuch_lastmod_strings_to_query (notmuch_database_t *notmuch,
+				   const std::string &from, const std::string &to,
+				   Xapian::Query &output, std::string &msg);
 #endif
 #endif
diff --git a/lib/lastmod-fp.cc b/lib/lastmod-fp.cc
new file mode 100644
index 00000000..5fdaf281
--- /dev/null
+++ b/lib/lastmod-fp.cc
@@ -0,0 +1,68 @@
+/* lastmod-fp.cc - lastmod range query glue
+ *
+ * This file is part of notmuch.
+ *
+ * Copyright © 2022 David Bremner
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see https://www.gnu.org/licenses/ .
+ *
+ * Author: David Bremner <david@tethera.net>
+ */
+
+#include "database-private.h"
+
+notmuch_status_t
+_notmuch_lastmod_strings_to_query (notmuch_database_t *notmuch,
+				   const std::string &from, const std::string &to,
+				   Xapian::Query &output, std::string &msg)
+{
+    long from_idx = 0L, to_idx = LONG_MAX;
+    long current;
+    std::string str;
+
+    /* revision should not change, but for the avoidance of doubt,
+     * grab for both ends of range, if needed*/
+    current = notmuch_database_get_revision (notmuch, NULL);
+
+    try {
+	if (from.empty ())
+	    from_idx = 0L;
+	else
+	    from_idx = std::stol (from);
+    } catch (std::logic_error &e) {
+	msg = "bad 'from' revision: '" + from + "'";
+	return NOTMUCH_STATUS_BAD_QUERY_SYNTAX;
+    }
+
+    if (from_idx < 0)
+	from_idx += current;
+
+    try {
+	if (EMPTY_STRING (to))
+	    to_idx = LONG_MAX;
+	else
+	    to_idx = std::stol (to);
+    } catch (std::logic_error &e) {
+	msg = "bad 'to' revision: '" + to + "'";
+	return NOTMUCH_STATUS_BAD_QUERY_SYNTAX;
+    }
+
+    if (to_idx < 0)
+	to_idx += current;
+
+    output = Xapian::Query (Xapian::Query::OP_VALUE_RANGE, NOTMUCH_VALUE_LAST_MOD,
+			    Xapian::sortable_serialise (from_idx),
+			    Xapian::sortable_serialise (to_idx));
+    return NOTMUCH_STATUS_SUCCESS;
+}
diff --git a/lib/parse-sexp.cc b/lib/parse-sexp.cc
index e9ef4268..9cadbc13 100644
--- a/lib/parse-sexp.cc
+++ b/lib/parse-sexp.cc
@@ -563,38 +563,13 @@ _sexp_parse_range (notmuch_database_t *notmuch,  const _sexp_prefix_t *prefix,
     }
 
     if (strcmp (prefix->name, "lastmod") == 0) {
-	long from_idx, to_idx;
-
-	try {
-	    if (EMPTY_STRING (from))
-		from_idx = 0L;
-	    else
-		from_idx = std::stol (from);
-	} catch (std::logic_error &e) {
-	    _notmuch_database_log (notmuch, "bad 'from' revision: '%s'\n", from);
-	    return NOTMUCH_STATUS_BAD_QUERY_SYNTAX;
+	notmuch_status_t status;
+	status = _notmuch_lastmod_strings_to_query (notmuch, from, to, output, msg);
+	if (status) {
+	    if (! msg.empty ())
+		_notmuch_database_log (notmuch, "%s\n", msg.c_str ());
 	}
-
-	if (from_idx < 0)
-	    from_idx += notmuch_database_get_revision (notmuch, NULL);
-
-	try {
-	    if (EMPTY_STRING (to))
-		to_idx = LONG_MAX;
-	    else
-		to_idx = std::stol (to);
-	} catch (std::logic_error &e) {
-	    _notmuch_database_log (notmuch, "bad 'to' revision: '%s'\n", to);
-	    return NOTMUCH_STATUS_BAD_QUERY_SYNTAX;
-	}
-
-	if (to_idx < 0)
-	    to_idx += notmuch_database_get_revision (notmuch, NULL);
-
-	output = Xapian::Query (Xapian::Query::OP_VALUE_RANGE, NOTMUCH_VALUE_LAST_MOD,
-				Xapian::sortable_serialise (from_idx),
-				Xapian::sortable_serialise (to_idx));
-	return NOTMUCH_STATUS_SUCCESS;
+	return status;
     }
 
     _notmuch_database_log (notmuch, "unimplimented range prefix: '%s'\n", prefix->name);