diff --git a/sstables/key.hh b/sstables/key.hh
index 8a3a1afe1f..f32426a55b 100644
--- a/sstables/key.hh
+++ b/sstables/key.hh
@@ -29,14 +29,10 @@ public:
         return ::with_linearized(_bytes, func);
     }
 
-    std::vector<bytes_view> explode(const schema& s) const {
-        return with_linearized([&] (bytes_view v) {
-            return composite_view(v, s.partition_key_size() > 1).explode();
-        });
-    }
-
     partition_key to_partition_key(const schema& s) const {
-        return partition_key::from_exploded_view(explode(s));
+        return with_linearized([&] (bytes_view v) {
+            return partition_key::from_exploded_view(composite_view(v, s.partition_key_size() > 1).explode());
+        });
     }
 
     bool operator==(const key_view& k) const = default;
diff --git a/sstables/kl/reader.cc b/sstables/kl/reader.cc
index 10783ff864..223d5148d0 100644
--- a/sstables/kl/reader.cc
+++ b/sstables/kl/reader.cc
@@ -412,7 +412,7 @@ public:
         if (!_is_mutation_end) {
             return proceed::yes;
         }
-        auto pk = partition_key::from_exploded(key.explode(*_schema));
+        auto pk = key.to_partition_key(*_schema);
         setup_for_partition(pk);
         auto dk = dht::decorate_key(*_schema, pk);
         _reader->on_next_partition(std::move(dk), tombstone(deltime));
diff --git a/sstables/mx/reader.cc b/sstables/mx/reader.cc
index 5e7614c13a..bbc968dd0e 100644
--- a/sstables/mx/reader.cc
+++ b/sstables/mx/reader.cc
@@ -309,7 +309,7 @@ public:
         if (!_is_mutation_end) {
             return data_consumer::proceed::yes;
         }
-        auto pk = partition_key::from_exploded(key.explode(*_schema));
+        auto pk = key.to_partition_key(*_schema);
         setup_for_partition(pk);
         auto dk = dht::decorate_key(*_schema, pk);
         _reader->on_next_partition(std::move(dk), tombstone(deltime));
@@ -1941,7 +1941,7 @@ public:
     }
 
     data_consumer::proceed consume_partition_start(sstables::key_view key, sstables::deletion_time deltime) {
-        auto pk = partition_key::from_exploded(key.explode(*_schema));
+        auto pk = key.to_partition_key(*_schema);
         auto dk = dht::decorate_key(*_schema, pk);
         _current_pos = position_in_partition(position_in_partition::partition_start_tag_t{});
         sstlog.trace("validating_consumer {}: {}({}) _expected_pkey={}", fmt::ptr(this), __FUNCTION__, pk, _expected_pkey);
diff --git a/test/cql-pytest/test_sstable.py b/test/cql-pytest/test_sstable.py
index a2796350d1..7ab0f9943e 100644
--- a/test/cql-pytest/test_sstable.py
+++ b/test/cql-pytest/test_sstable.py
@@ -14,6 +14,7 @@
 import pytest
 from util import unique_name, new_test_table
 import nodetool
+import random
 
 # Reproduces issue #8138, where the sstable reader in a TWCS sstable set
 # had a bug and resulted in no results for queries.
@@ -36,3 +37,21 @@ def test_twcs_optimal_query_path(cql, test_keyspace, scylla_only):
         # in the debug build.
         nodetool.flush(cql, table)
         assert 1 == len(list(cql.execute(f"SELECT * FROM {table} WHERE pk = 0 BYPASS CACHE")))
+
+# Reproduces https://github.com/scylladb/scylladb/issues/17625.
+# Without the fix, it trips ASAN.
+def test_big_key_index_reader(cql, test_keyspace, scylla_only):
+    with new_test_table(cql, test_keyspace, "pk blob, ck blob, PRIMARY KEY (pk, ck)") as table:
+        # Insert a partition with a partition key large enough to be fragmented in LSA,
+        # and enough clustering rows for a promoted index to be written.
+        insert = cql.prepare(f"INSERT INTO {table}(pk, ck) VALUES(?, ?)")
+        k = 30000
+        pk = random.randbytes(k)
+        for i in range(10):
+            ck = random.randbytes(k)
+            cql.execute(insert, [pk, ck])
+        # Flush the partition.
+        nodetool.flush(cql, table)
+        # Read the partition from sstables.
+        select = cql.prepare(f"SELECT pk, ck FROM {table} WHERE pk = ? BYPASS CACHE")
+        cql.execute(select, [pk])