diff --git a/src/basic/string-util.c b/src/basic/string-util.c
index 7188625ad6e..1dc90d538ad 100644
--- a/src/basic/string-util.c
+++ b/src/basic/string-util.c
@@ -287,6 +287,12 @@ static size_t previous_ansi_sequence(const char *s, size_t length, const char **
 
         /* Locate the previous ANSI sequence and save its start in *ret_where and return length. */
 
+        if (length < 2) {
+                /* Need at least two bytes for an ANSI sequence */
+                *ret_where = NULL;
+                return 0;
+        }
+
         for (size_t i = length - 2; i > 0; i--) {  /* -2 because at least two bytes are needed */
                 size_t slen = ansi_sequence_length(s + (i - 1), length - (i - 1));
                 if (slen == 0)
diff --git a/src/basic/uid-range.c b/src/basic/uid-range.c
index 8771ad964bb..4d2c246dcd1 100644
--- a/src/basic/uid-range.c
+++ b/src/basic/uid-range.c
@@ -395,9 +395,18 @@ int uid_range_partition(UIDRange *range, uid_t size) {
         if (n_new_entries > range->n_entries && !GREEDY_REALLOC(range->entries, n_new_entries))
                 return -ENOMEM;
 
-        /* Work backwards to avoid overwriting entries we still need to read */
+        /* Compact in place: drop entries that contribute zero partitions (nr < size). This forward pass
+         * reads each entry once and only writes to lower-or-equal indices, so it cannot alias an unread
+         * source entry. */
+        size_t n_src = 0;
+        for (size_t i = 0; i < range->n_entries; i++)
+                if (range->entries[i].nr >= size)
+                        range->entries[n_src++] = range->entries[i];
+
+        /* Pre-compaction guarantees every surviving entry contributes at least one partition slot, so the
+         * write cursor t stays ahead of the read index. */
         size_t t = n_new_entries;
-        for (size_t i = range->n_entries; i > 0; i--) {
+        for (size_t i = n_src; i > 0; i--) {
                 UIDRangeEntry *e = range->entries + i - 1;
                 unsigned n_parts = e->nr / size;
 
diff --git a/src/test/test-string-util.c b/src/test/test-string-util.c
index 51f63963a96..970421c7abb 100644
--- a/src/test/test-string-util.c
+++ b/src/test/test-string-util.c
@@ -9,6 +9,17 @@
 #include "strv.h"
 #include "tests.h"
 
+TEST(ellipsize_mem_ansi_short) {
+        _cleanup_free_ char *a = ellipsize_mem("X\x1b[m", 4, 1, 50);
+        assert_se(a);
+
+        _cleanup_free_ char *b = ellipsize_mem(" \x1b[A", 4, 1, 0);
+        assert_se(b);
+
+        _cleanup_free_ char *c = ellipsize_mem("\x1b[m", 3, 1, 50);
+        assert_se(c);
+}
+
 TEST(xsprintf) {
         char buf[5];
 
diff --git a/src/test/test-uid-range.c b/src/test/test-uid-range.c
index 6eef98153ef..fdcbd8896e8 100644
--- a/src/test/test-uid-range.c
+++ b/src/test/test-uid-range.c
@@ -318,6 +318,68 @@ TEST(uid_range_partition) {
 
         p = uid_range_free(p);
 
+        /* Small entry preceding a large entry: the small entry must be dropped and the large entry
+         * partitioned without the in-place backward-fill write cursor aliasing the still-live small entry
+         * slot. */
+        ASSERT_OK(uid_range_add_str(&p, "0-4"));
+        ASSERT_OK(uid_range_add_str(&p, "100-129"));
+        ASSERT_EQ(uid_range_entries(p), 2U);
+        ASSERT_OK(uid_range_partition(p, 10));
+        ASSERT_EQ(uid_range_entries(p), 3U);
+        ASSERT_EQ(p->entries[0].start, 100U);
+        ASSERT_EQ(p->entries[0].nr, 10U);
+        ASSERT_EQ(p->entries[1].start, 110U);
+        ASSERT_EQ(p->entries[1].nr, 10U);
+        ASSERT_EQ(p->entries[2].start, 120U);
+        ASSERT_EQ(p->entries[2].nr, 10U);
+
+        p = uid_range_free(p);
+
+        /* A too-small entry between two partitionable entries is dropped; the others still partition. */
+        ASSERT_OK(uid_range_add_str(&p, "0-4"));        /* nr=5  < size -> dropped */
+        ASSERT_OK(uid_range_add_str(&p, "50-69"));      /* nr=20       -> 2 parts */
+        ASSERT_OK(uid_range_add_str(&p, "200-204"));    /* nr=5  < size -> dropped */
+        ASSERT_OK(uid_range_add_str(&p, "1000-1029"));  /* nr=30       -> 3 parts */
+        ASSERT_EQ(uid_range_entries(p), 4U);
+        ASSERT_OK(uid_range_partition(p, 10));
+        ASSERT_EQ(uid_range_entries(p), 5U);
+        ASSERT_EQ(p->entries[0].start, 50U);
+        ASSERT_EQ(p->entries[0].nr, 10U);
+        ASSERT_EQ(p->entries[1].start, 60U);
+        ASSERT_EQ(p->entries[1].nr, 10U);
+        ASSERT_EQ(p->entries[2].start, 1000U);
+        ASSERT_EQ(p->entries[2].nr, 10U);
+        ASSERT_EQ(p->entries[3].start, 1010U);
+        ASSERT_EQ(p->entries[3].nr, 10U);
+        ASSERT_EQ(p->entries[4].start, 1020U);
+        ASSERT_EQ(p->entries[4].nr, 10U);
+
+        p = uid_range_free(p);
+
+        /* A too-small entry before a partitionable entry is dropped. */
+        ASSERT_OK(uid_range_add_str(&p, "0-4"));        /* nr=5  < size -> dropped */
+        ASSERT_OK(uid_range_add_str(&p, "100-119"));    /* nr=20       -> 2 parts */
+        ASSERT_OK(uid_range_partition(p, 10));
+        ASSERT_EQ(uid_range_entries(p), 2U);
+        ASSERT_EQ(p->entries[0].start, 100U);
+        ASSERT_EQ(p->entries[0].nr, 10U);
+        ASSERT_EQ(p->entries[1].start, 110U);
+        ASSERT_EQ(p->entries[1].nr, 10U);
+
+        p = uid_range_free(p);
+
+        /* A too-small entry after a partitionable entry is dropped. */
+        ASSERT_OK(uid_range_add_str(&p, "0-199"));      /* nr=200 -> 2 parts */
+        ASSERT_OK(uid_range_add_str(&p, "1000-1004"));  /* nr=5  < size -> dropped */
+        ASSERT_OK(uid_range_partition(p, 100));
+        ASSERT_EQ(uid_range_entries(p), 2U);
+        ASSERT_EQ(p->entries[0].start, 0U);
+        ASSERT_EQ(p->entries[0].nr, 100U);
+        ASSERT_EQ(p->entries[1].start, 100U);
+        ASSERT_EQ(p->entries[1].nr, 100U);
+
+        p = uid_range_free(p);
+
         /* Partition size of 1 */
         ASSERT_OK(uid_range_add_str(&p, "100-102"));
         ASSERT_OK(uid_range_partition(p, 1));