diff --git a/src/analyze/analyze.c b/src/analyze/analyze.c
index a28b27a3a0..4ebce83b2c 100644
--- a/src/analyze/analyze.c
+++ b/src/analyze/analyze.c
@@ -1568,7 +1568,7 @@ static int do_unit_files(int argc, char *argv[], void *userdata) {
         if (r < 0)
                 return log_error_errno(r, "lookup_paths_init() failed: %m");
 
-        r = unit_file_build_name_map(&lp, &unit_ids, &unit_names, NULL);
+        r = unit_file_build_name_map(&lp, NULL, &unit_ids, &unit_names, NULL);
         if (r < 0)
                 return log_error_errno(r, "unit_file_build_name_map() failed: %m");
 
diff --git a/src/core/load-fragment.c b/src/core/load-fragment.c
index 7521d599e9..f34e424fbc 100644
--- a/src/core/load-fragment.c
+++ b/src/core/load-fragment.c
@@ -4611,6 +4611,15 @@ int unit_load_fragment(Unit *u) {
                 return 0;
         }
 
+        /* Possibly rebuild the fragment map to catch new units */
+        r = unit_file_build_name_map(&u->manager->lookup_paths,
+                                     &u->manager->unit_cache_mtime,
+                                     &u->manager->unit_id_map,
+                                     &u->manager->unit_name_map,
+                                     &u->manager->unit_path_cache);
+        if (r < 0)
+                log_error_errno(r, "Failed to rebuild name map: %m");
+
         r = unit_file_find_fragment(u->manager->unit_id_map,
                                     u->manager->unit_name_map,
                                     u->id,
diff --git a/src/core/manager.c b/src/core/manager.c
index f8a7e7d64e..4a503a944e 100644
--- a/src/core/manager.c
+++ b/src/core/manager.c
@@ -678,6 +678,7 @@ static void manager_free_unit_name_maps(Manager *m) {
         m->unit_id_map = hashmap_free(m->unit_id_map);
         m->unit_name_map = hashmap_free(m->unit_name_map);
         m->unit_path_cache = set_free_free(m->unit_path_cache);
+        m->unit_cache_mtime =  0;
 }
 
 static int manager_setup_run_queue(Manager *m) {
@@ -1626,11 +1627,6 @@ int manager_startup(Manager *m, FILE *serialization, FDSet *fds) {
         if (r < 0)
                 log_warning_errno(r, "Failed to reduce unit file paths, ignoring: %m");
 
-        manager_free_unit_name_maps(m);
-        r = unit_file_build_name_map(&m->lookup_paths, &m->unit_id_map, &m->unit_name_map, &m->unit_path_cache);
-        if (r < 0)
-                return log_error_errno(r, "Failed to build name map: %m");
-
         {
                 /* This block is (optionally) done with the reloading counter bumped */
                 _cleanup_(manager_reloading_stopp) Manager *reloading = NULL;
@@ -2847,10 +2843,6 @@ int manager_loop(Manager *m) {
         assert(m);
         assert(m->objective == MANAGER_OK); /* Ensure manager_startup() has been called */
 
-        /* Release the path and unit name caches */
-        manager_free_unit_name_maps(m);
-        // FIXME: once this happens, we cannot load any more units
-
         manager_check_finished(m);
 
         /* There might still be some zombies hanging around from before we were exec()'ed. Let's reap them. */
@@ -3526,10 +3518,8 @@ int manager_reload(Manager *m) {
         if (r < 0)
                 log_warning_errno(r, "Failed to reduce unit file paths, ignoring: %m");
 
+        /* We flushed out generated files, for which we don't watch mtime, so we should flush the old map. */
         manager_free_unit_name_maps(m);
-        r = unit_file_build_name_map(&m->lookup_paths, &m->unit_id_map, &m->unit_name_map, &m->unit_path_cache);
-        if (r < 0)
-                log_warning_errno(r, "Failed to build name map: %m");
 
         /* First, enumerate what we can from kernel and suchlike */
         manager_enumerate_perpetual(m);
diff --git a/src/core/manager.h b/src/core/manager.h
index 3cb37b3bf4..596220848f 100644
--- a/src/core/manager.h
+++ b/src/core/manager.h
@@ -224,6 +224,7 @@ struct Manager {
         Hashmap *unit_id_map;
         Hashmap *unit_name_map;
         Set *unit_path_cache;
+        usec_t unit_cache_mtime;
 
         char **transient_environment;  /* The environment, as determined from config files, kernel cmdline and environment generators */
         char **client_environment;     /* Environment variables created by clients through the bus API */
diff --git a/src/shared/unit-file.c b/src/shared/unit-file.c
index 90fa949d24..8a09f3827f 100644
--- a/src/shared/unit-file.c
+++ b/src/shared/unit-file.c
@@ -152,8 +152,47 @@ static int unit_ids_map_get(
         return -ELOOP;
 }
 
+static bool lookup_paths_mtime_exclude(const LookupPaths *lp, const char *path) {
+        /* Paths that are under our exclusive control. Users shall not alter those directly. */
+
+        return streq_ptr(path, lp->generator) ||
+               streq_ptr(path, lp->generator_early) ||
+               streq_ptr(path, lp->generator_late) ||
+               streq_ptr(path, lp->transient) ||
+               streq_ptr(path, lp->persistent_control) ||
+               streq_ptr(path, lp->runtime_control);
+}
+
+static bool lookup_paths_mtime_good(const LookupPaths *lp, usec_t mtime) {
+        char **dir;
+
+        STRV_FOREACH(dir, (char**) lp->search_path) {
+                struct stat st;
+
+                if (lookup_paths_mtime_exclude(lp, *dir))
+                        continue;
+
+                /* Determine the latest lookup path modification time */
+                if (stat(*dir, &st) < 0) {
+                        if (errno == ENOENT)
+                                continue;
+
+                        log_debug_errno(errno, "Failed to stat %s, ignoring: %m", *dir);
+                        continue;
+                }
+
+                if (timespec_load(&st.st_mtim) > mtime) {
+                        log_debug_errno(errno, "Unit dir %s has changed, need to update cache.", *dir);
+                        return false;
+                }
+        }
+
+        return true;
+}
+
 int unit_file_build_name_map(
                 const LookupPaths *lp,
+                usec_t *cache_mtime,
                 Hashmap **ret_unit_ids_map,
                 Hashmap **ret_unit_names_map,
                 Set **ret_path_cache) {
@@ -171,6 +210,12 @@ int unit_file_build_name_map(
         _cleanup_set_free_free_ Set *paths = NULL;
         char **dir;
         int r;
+        usec_t mtime = 0;
+
+        /* Before doing anything, check if the mtime that was passed is still valid. If
+         * yes, do nothing. If *cache_time == 0, always build the cache. */
+        if (cache_mtime && *cache_mtime > 0 && lookup_paths_mtime_good(lp, *cache_mtime))
+                return 0;
 
         if (ret_path_cache) {
                 paths = set_new(&path_hash_ops);
@@ -181,6 +226,7 @@ int unit_file_build_name_map(
         STRV_FOREACH(dir, (char**) lp->search_path) {
                 struct dirent *de;
                 _cleanup_closedir_ DIR *d = NULL;
+                struct stat st;
 
                 d = opendir(*dir);
                 if (!d) {
@@ -189,6 +235,13 @@ int unit_file_build_name_map(
                         continue;
                 }
 
+                /* Determine the latest lookup path modification time */
+                if (fstat(dirfd(d), &st) < 0)
+                        return log_error_errno(errno, "Failed to fstat %s: %m", *dir);
+
+                if (!lookup_paths_mtime_exclude(lp, *dir))
+                        mtime = MAX(mtime, timespec_load(&st.st_mtim));
+
                 FOREACH_DIRENT(de, d, log_warning_errno(errno, "Failed to read \"%s\", ignoring: %m", *dir)) {
                         char *filename;
                         _cleanup_free_ char *_filename_free = NULL, *simplified = NULL;
@@ -316,12 +369,14 @@ int unit_file_build_name_map(
                                                  basename(dst), src);
         }
 
+        if (cache_mtime)
+                *cache_mtime = mtime;
         *ret_unit_ids_map = TAKE_PTR(ids);
         *ret_unit_names_map = TAKE_PTR(names);
         if (ret_path_cache)
                 *ret_path_cache = TAKE_PTR(paths);
 
-        return 0;
+        return 1;
 }
 
 int unit_file_find_fragment(
diff --git a/src/shared/unit-file.h b/src/shared/unit-file.h
index 52e17f7cfb..54cc7876fe 100644
--- a/src/shared/unit-file.h
+++ b/src/shared/unit-file.h
@@ -4,6 +4,7 @@
 #include <stdbool.h>
 
 #include "hashmap.h"
+#include "time-util.h"
 #include "unit-name.h"
 
 typedef enum UnitFileState UnitFileState;
@@ -42,6 +43,7 @@ int unit_validate_alias_symlink_and_warn(const char *filename, const char *targe
 
 int unit_file_build_name_map(
                 const LookupPaths *lp,
+                usec_t *ret_time,
                 Hashmap **ret_unit_ids_map,
                 Hashmap **ret_unit_names_map,
                 Set **ret_path_cache);
diff --git a/src/systemctl/systemctl.c b/src/systemctl/systemctl.c
index 31d364cefe..1140deb0d1 100644
--- a/src/systemctl/systemctl.c
+++ b/src/systemctl/systemctl.c
@@ -2593,7 +2593,7 @@ static int unit_find_paths(
                 _cleanup_set_free_free_ Set *names = NULL;
 
                 if (!cached_name_map) {
-                        r = unit_file_build_name_map(lp, &cached_id_map, &cached_name_map, NULL);
+                        r = unit_file_build_name_map(lp, NULL, &cached_id_map, &cached_name_map, NULL);
                         if (r < 0)
                                 return r;
                 }
diff --git a/src/test/test-unit-file.c b/src/test/test-unit-file.c
index c5144a1b7e..0c0371375a 100644
--- a/src/test/test-unit-file.c
+++ b/src/test/test-unit-file.c
@@ -31,10 +31,12 @@ static void test_unit_file_build_name_map(void) {
         Iterator i;
         const char *k, *dst;
         char **v;
+        usec_t mtime = 0;
+        int r;
 
         assert_se(lookup_paths_init(&lp, UNIT_FILE_SYSTEM, 0, NULL) >= 0);
 
-        assert_se(unit_file_build_name_map(&lp, &unit_ids, &unit_names, NULL) == 0);
+        assert_se(unit_file_build_name_map(&lp, &mtime, &unit_ids, &unit_names, NULL) == 1);
 
         HASHMAP_FOREACH_KEY(dst, k, unit_ids, i)
                 log_info("ids: %s → %s", k, dst);
@@ -43,6 +45,14 @@ static void test_unit_file_build_name_map(void) {
                 _cleanup_free_ char *j = strv_join(v, ", ");
                 log_info("aliases: %s ← %s", k, j);
         }
+
+        char buf[FORMAT_TIMESTAMP_MAX];
+        log_debug("Last modification time: %s", format_timestamp(buf, sizeof buf, mtime));
+
+        r = unit_file_build_name_map(&lp, &mtime, &unit_ids, &unit_names, NULL);
+        assert_se(IN_SET(r, 0, 1));
+        if (r == 0)
+                log_debug("Cache rebuild skipped based on mtime.");
 }
 
 int main(int argc, char **argv) {