diff --git a/okapi-core/src/main/kotlin/com/softwaremill/okapi/core/OutboxStore.kt b/okapi-core/src/main/kotlin/com/softwaremill/okapi/core/OutboxStore.kt
index 07c60e5..8b21a11 100644
--- a/okapi-core/src/main/kotlin/com/softwaremill/okapi/core/OutboxStore.kt
+++ b/okapi-core/src/main/kotlin/com/softwaremill/okapi/core/OutboxStore.kt
@@ -24,7 +24,7 @@ interface OutboxStore {
      * [OutboxEntry.createdAt] of its oldest entry (the minimum `createdAt` among entries in
      * that status). Statuses with no entries are omitted from the result -- callers rely on
      * absence to mean "no backlog" (e.g. the lag gauge reports 0 for an omitted status).
-     * Useful for lag metrics.
+     * An empty [statuses] set returns an empty map.
      */
     fun findOldestCreatedAt(statuses: Set<OutboxStatus>): Map<OutboxStatus, Instant>
 
diff --git a/okapi-integration-tests/src/test/kotlin/com/softwaremill/okapi/test/store/OutboxStoreContractTests.kt b/okapi-integration-tests/src/test/kotlin/com/softwaremill/okapi/test/store/OutboxStoreContractTests.kt
index 6550a91..02d1394 100644
--- a/okapi-integration-tests/src/test/kotlin/com/softwaremill/okapi/test/store/OutboxStoreContractTests.kt
+++ b/okapi-integration-tests/src/test/kotlin/com/softwaremill/okapi/test/store/OutboxStoreContractTests.kt
@@ -246,6 +246,16 @@ fun FunSpec.outboxStoreContractTests(
         oldest.keys shouldBe setOf(OutboxStatus.PENDING)
     }
 
+    test("[$dbName] findOldestCreatedAt returns an empty map for an empty statuses set") {
+        // Regression guard (issue #60): an empty `statuses` set used to build `WHERE status IN ()`,
+        // a syntax error on both Postgres and MySQL. Must short-circuit to emptyMap() instead.
+        jdbc.withTransaction { store.persist(createTestEntry()) }
+
+        val oldest = jdbc.withTransaction { store.findOldestCreatedAt(emptySet()) }
+
+        oldest shouldBe emptyMap()
+    }
+
     test("[$dbName] claimPending returns empty when no PENDING entries") {
         val claimed = jdbc.withTransaction { store.claimPending(10) }
 
diff --git a/okapi-mysql/src/main/kotlin/com/softwaremill/okapi/mysql/MysqlOutboxStore.kt b/okapi-mysql/src/main/kotlin/com/softwaremill/okapi/mysql/MysqlOutboxStore.kt
index b611a5b..38a84bd 100644
--- a/okapi-mysql/src/main/kotlin/com/softwaremill/okapi/mysql/MysqlOutboxStore.kt
+++ b/okapi-mysql/src/main/kotlin/com/softwaremill/okapi/mysql/MysqlOutboxStore.kt
@@ -34,9 +34,9 @@ class MysqlOutboxStore(
                         Timestamp.from(entry.lastAttempt),
                     )
                 } else {
-                    stmt.setNull(9, java.sql.Types.TIMESTAMP)
+                    stmt.setNull(9, Types.TIMESTAMP)
                 }
-                if (entry.lastError != null) stmt.setString(10, entry.lastError) else stmt.setNull(10, java.sql.Types.VARCHAR)
+                if (entry.lastError != null) stmt.setString(10, entry.lastError) else stmt.setNull(10, Types.VARCHAR)
                 stmt.setString(11, entry.deliveryMetadata)
                 stmt.executeUpdate()
             }
@@ -102,6 +102,8 @@ class MysqlOutboxStore(
     }
 
     override fun findOldestCreatedAt(statuses: Set<OutboxStatus>): Map<OutboxStatus, Instant> {
+        if (statuses.isEmpty()) return emptyMap()
+
         val result = mutableMapOf<OutboxStatus, Instant>()
         val placeholders = statuses.joinToString(",") { "?" }
         val sql = "SELECT status, MIN(created_at) AS min_created_at FROM okapi_outbox WHERE status IN ($placeholders) GROUP BY status"
diff --git a/okapi-postgres/src/main/kotlin/com/softwaremill/okapi/postgres/PostgresOutboxStore.kt b/okapi-postgres/src/main/kotlin/com/softwaremill/okapi/postgres/PostgresOutboxStore.kt
index 0d23a71..0ee29f5 100644
--- a/okapi-postgres/src/main/kotlin/com/softwaremill/okapi/postgres/PostgresOutboxStore.kt
+++ b/okapi-postgres/src/main/kotlin/com/softwaremill/okapi/postgres/PostgresOutboxStore.kt
@@ -34,9 +34,9 @@ class PostgresOutboxStore(
                         Timestamp.from(entry.lastAttempt),
                     )
                 } else {
-                    stmt.setNull(9, java.sql.Types.TIMESTAMP)
+                    stmt.setNull(9, Types.TIMESTAMP)
                 }
-                if (entry.lastError != null) stmt.setString(10, entry.lastError) else stmt.setNull(10, java.sql.Types.VARCHAR)
+                if (entry.lastError != null) stmt.setString(10, entry.lastError) else stmt.setNull(10, Types.VARCHAR)
                 stmt.setString(11, entry.deliveryMetadata)
                 stmt.executeUpdate()
             }
@@ -96,6 +96,8 @@ class PostgresOutboxStore(
     }
 
     override fun findOldestCreatedAt(statuses: Set<OutboxStatus>): Map<OutboxStatus, Instant> {
+        if (statuses.isEmpty()) return emptyMap()
+
         val result = mutableMapOf<OutboxStatus, Instant>()
         val placeholders = statuses.joinToString(",") { "?" }
         val sql = "SELECT status, MIN(created_at) AS min_created_at FROM okapi_outbox WHERE status IN ($placeholders) GROUP BY status"