diff --git a/fsmonitor.c b/fsmonitor.c
index 292a6742b4..e1229c289c 100644
--- a/fsmonitor.c
+++ b/fsmonitor.c
@@ -184,30 +184,68 @@ static int query_fsmonitor_hook(struct repository *r,
 static void fsmonitor_refresh_callback(struct index_state *istate, char *name)
 {
 	int i, len = strlen(name);
-	if (name[len - 1] == '/') {
+	int pos = index_name_pos(istate, name, len);
+
+	trace_printf_key(&trace_fsmonitor,
+			 "fsmonitor_refresh_callback '%s' (pos %d)",
+			 name, pos);
 
+	if (name[len - 1] == '/') {
 		/*
-		 * TODO We should binary search to find the first path with
-		 * TODO this directory prefix.  Then linearly update entries
-		 * TODO while the prefix matches.  Taking care to search without
-		 * TODO the trailing slash -- because '/' sorts after a few
-		 * TODO interesting special chars, like '.' and ' '.
+		 * The daemon can decorate directory events, such as
+		 * moves or renames, with a trailing slash if the OS
+		 * FS Event contains sufficient information, such as
+		 * MacOS.
+		 *
+		 * Use this to invalidate the entire cone under that
+		 * directory.
+		 *
+		 * We do not expect an exact match because the index
+		 * does not normally contain directory entries, so we
+		 * start at the insertion point and scan.
 		 */
+		if (pos < 0)
+			pos = -pos - 1;
 
 		/* Mark all entries for the folder invalid */
-		for (i = 0; i < istate->cache_nr; i++) {
-			if (istate->cache[i]->ce_flags & CE_FSMONITOR_VALID &&
-			    starts_with(istate->cache[i]->name, name))
-				istate->cache[i]->ce_flags &= ~CE_FSMONITOR_VALID;
+		for (i = pos; i < istate->cache_nr; i++) {
+			if (!starts_with(istate->cache[i]->name, name))
+				break;
+			istate->cache[i]->ce_flags &= ~CE_FSMONITOR_VALID;
 		}
-		/* Need to remove the / from the path for the untracked cache */
+
+		/*
+		 * We need to remove the traling "/" from the path
+		 * for the untracked cache.
+		 */
 		name[len - 1] = '\0';
+	} else if (pos >= 0) {
+		/*
+		 * We have an exact match for this path and can just
+		 * invalidate it.
+		 */
+		istate->cache[pos]->ce_flags &= ~CE_FSMONITOR_VALID;
 	} else {
-		int pos = index_name_pos(istate, name, strlen(name));
-
-		if (pos >= 0) {
-			struct cache_entry *ce = istate->cache[pos];
-			ce->ce_flags &= ~CE_FSMONITOR_VALID;
+		/*
+		 * The path is not a tracked file -or- it is a
+		 * directory event on a platform that cannot
+		 * distinguish between file and directory events in
+		 * the event handler, such as Windows.
+		 *
+		 * Scan as if it is a directory and invalidate the
+		 * cone under it.  (But remember to ignore items
+		 * between "name" and "name/", such as "name-" and
+		 * "name.".
+		 */
+		pos = -pos - 1;
+
+		for (i = pos; i < istate->cache_nr; i++) {
+			if (!starts_with(istate->cache[i]->name, name))
+				break;
+			if ((unsigned char)istate->cache[i]->name[len] > '/')
+				break;
+			if (istate->cache[i]->name[len] == '/')
+				istate->cache[i]->ce_flags &= ~CE_FSMONITOR_VALID;
 		}
 	}
 
@@ -215,7 +253,6 @@ static void fsmonitor_refresh_callback(struct index_state *istate, char *name)
 	 * Mark the untracked cache dirty even if it wasn't found in the index
 	 * as it could be a new untracked file.
 	 */
-	trace_printf_key(&trace_fsmonitor, "fsmonitor_refresh_callback '%s'", name);
 	untracked_cache_invalidate_path(istate, name, 0);
 }