diff --git a/lib/mu-indexer.cc b/lib/mu-indexer.cc
index 12ff06a45..a658ada3d 100644
--- a/lib/mu-indexer.cc
+++ b/lib/mu-indexer.cc
@@ -145,6 +145,8 @@ struct Indexer::Private {
 	std::mutex lock_, w_lock_;
 	std::atomic<time_t> completed_{};
 	bool was_empty_{};
+
+	uint64_t last_index_{};
 };
 
 bool
@@ -206,12 +208,16 @@ Indexer::Private::handler(const std::string& fullpath, struct stat* statbuf,
 
 	case Scanner::HandleType::File: {
 		++progress_.checked;
+		if (conf_.lazy_check && static_cast<uint64_t>(statbuf->st_ctime) < last_index_) {
+			// in lazy mode, ignore the file if it has not changed
+			// since the last indexing op.
+			return false;
+		}
 
-		if ((size_t)statbuf->st_size > max_message_size_) {
+		if (static_cast<size_t>(statbuf->st_size) > max_message_size_) {
 			mu_debug("skip {} (too big: {} bytes)", fullpath, statbuf->st_size);
 			return false;
 		}
-
 		// if the message is not in the db yet, or not up-to-date, queue
 		// it for updating/inserting.
 		if (statbuf->st_ctime <= dirstamp_ && store_.contains_message(fullpath))
@@ -414,6 +420,10 @@ Indexer::Private::start(const Indexer::Config& conf, bool block)
 	mu_debug("indexing: {}; clean-up: {}", conf_.scan ? "yes" : "no",
 		 conf_.cleanup ? "yes" : "no");
 
+	// remember the _previous_ indexing, so in lazy mode we can skip
+	// those files.
+	last_index_ = store_.config().get<Mu::Config::Id::LastIndex>();
+
 	state_.change_to(IndexState::Scanning);
 	/* kick off the first worker, which will spawn more if needed. */
 	workers_.emplace_back(std::thread([this] { item_worker(); }));
diff --git a/lib/mu-indexer.hh b/lib/mu-indexer.hh
index 3ea1fb632..7fa24169b 100644
--- a/lib/mu-indexer.hh
+++ b/lib/mu-indexer.hh
@@ -54,8 +54,8 @@ public:
 		bool ignore_noupdate{};
 		/**< ignore .noupdate files */
 		bool lazy_check{};
-		/**< whether to skip directories that don't have a changed
-		 * mtime */
+		/**< whether to skip directories or message files that haven't changed since the
+		 * previous indexing operation, based on their ctime */
 	};
 
 	/**
diff --git a/man/mu-index.1.org b/man/mu-index.1.org
index 5ddb35b77..af49eb023 100644
--- a/man/mu-index.1.org
+++ b/man/mu-index.1.org
@@ -41,7 +41,7 @@ If there is a file called _.noupdate_ in a directory, the contents of that
 directory and all of its subdirectories will be ignored. This can be useful to
 speed up things you have some maildirs that never change.
 
-_.noupdate_ does not affect already-indexed message: you can still search for
+_.noupdate_ does not affect already-indexed messages: you can still search for
 them. _.noupdate_ is ignored when you start indexing with an empty database (such
 as directly after *mu init*).
 
@@ -58,7 +58,7 @@ the database for which there is no longer a corresponding file in the Maildir.
 If you do not want this, you can use *-n*, *--nocleanup*.
 
 When *mu index* catches one of the signals *SIGINT*, *SIGHUP* or *SIGTERM* (e.g., when
-you press Ctrl-C during the indexing process), it attempts to shutdown
+you press *Ctrl-C* during the indexing process), it attempts to shutdown
 gracefully; it tries to save and commit data, and close the database etc. If it
 receives another signal (e.g., when pressing Ctrl-C once more), *mu index* will
 terminate immediately.
@@ -67,12 +67,17 @@ terminate immediately.
 
 ** --lazy-check
 In lazy-check mode, *mu* does not consider messages for which the time-stamp
-(ctime) of the directory they reside in has not changed since the previous
-indexing run. This is much faster than the non-lazy check, but won't update
-messages that have change (rather than having been added or removed), since
-merely editing a message does not update the directory time-stamp. Of course,
-you can run *mu-index* occasionally without *--lazy-check*, to pick up such
-messages.
+(*ctime*) of the directory in which they reside, has not changed since the
+previous time this directory was checked.
+
+This is much faster than the non-lazy check, but won't update messages that have
+changed (rather than having been added or removed), since merely editing a
+message does not update the directory time-stamp. Of course, you can run
+*mu-index* occasionally without *--lazy-check*, to pick up such messages.
+
+Furthermore, in lazy-check mode, files which have a *ctime* smaller than the time
+the previous indexing operation was completed, are ignored. This helps for the
+use-case where new messages can appear in big maildirs.
 
 ** --nocleanup
 Disable the database cleanup that *mu* does by default after indexing.
@@ -172,7 +177,7 @@ The instructions are a little different since we have a proper repeatable
 benchmark now. After building,
 
 #+begin_example
- $ sudo sh -c 'sync && echo 3 > /proc/sys/vm/drop_caches'
+$ sudo sh -c 'sync && echo 3 > /proc/sys/vm/drop_caches'
 % THREAD_NUM=4 build/lib/tests/bench-indexer -m perf
 # random seed: R02Sf5c50e4851ec51adaf301e0e054bd52b
 1..1
@@ -185,7 +190,7 @@ ok 1 /bench/indexer/4-cores
 #+end_example
 
 Things are again a little faster, even though the index does a lot more now
-(text-normalizatian, and pre-generating message-sexps). A faster machine helps,
+(text-normalization, and pre-generating message-sexps). A faster machine helps,
 too!
 
 ** recent releases