diff --git a/.changeset/fair-seals-check.md b/.changeset/fair-seals-check.md
new file mode 100644
index 0000000000..f1ee8041bb
--- /dev/null
+++ b/.changeset/fair-seals-check.md
@@ -0,0 +1,5 @@
+---
+"effect": patch
+---
+
+Fix PostgreSQL shard advisory lock collisions across disjoint shard groups.
diff --git a/.gitignore b/.gitignore
index c0723a42a0..2860cf441f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -37,3 +37,9 @@ scratchpad/**/*
 
 # Codex
 .agents/
+
+# OpenCode
+.opencode/session-logs
+.opencode/plugins
+.opencode/package-lock.json
+opencode.jsonc
diff --git a/packages/effect/src/unstable/cluster/SqlRunnerStorage.ts b/packages/effect/src/unstable/cluster/SqlRunnerStorage.ts
index 8cfb747cea..2928f310da 100644
--- a/packages/effect/src/unstable/cluster/SqlRunnerStorage.ts
+++ b/packages/effect/src/unstable/cluster/SqlRunnerStorage.ts
@@ -283,15 +283,18 @@ export const make = Effect.fnUntraced(function*(options: {
       return Effect.fnUntraced(function*(_address: string, shardIds: ReadonlyArray<string>) {
         const [conn, pid] = yield* lockConn!.await
         const acquiredShardIds: Array<string> = []
-        const toAcquire = new Map(shardIds.map((shardId) => [lockNumbers.get(shardId)!, shardId]))
-        const takenLocks = yield* conn.executeValues(
-          `SELECT objid FROM pg_locks WHERE locktype = 'advisory' AND granted = true AND pid = ${pid} ORDER BY objid`,
-          []
+        const toAcquire = new Set(shardIds)
+        const takenLocks = yield* conn.executeUnprepared(
+          `SELECT ${pgHeldLocks(shardIds, pid)}`,
+          [],
+          undefined
         )
-        for (let i = 0; i < takenLocks.length; i++) {
-          const lockNum = takenLocks[i][0] as number
-          acquiredShardIds.push(lockNumbersReverse.get(lockNum)!)
-          toAcquire.delete(lockNum)
+        const heldLocks = takenLocks[0] as Record<string, boolean>
+        for (const shardId in heldLocks) {
+          if (heldLocks[shardId]) {
+            acquiredShardIds.push(shardId)
+            toAcquire.delete(shardId)
+          }
         }
         if (toAcquire.size === 0) {
           return acquiredShardIds
@@ -389,19 +392,6 @@ export const make = Effect.fnUntraced(function*(options: {
     }
   })
 
-  const lockNumbers = new Map<string, number>()
-  const lockNumbersReverse = new Map<number, string>()
-  for (let i = 0; i < config.shardGroups.length; i++) {
-    const group = config.shardGroups[i]
-    const base = (i + 1) * 1000000
-    for (let shard = 1; shard <= config.shardsPerGroup; shard++) {
-      const shardId = ShardId.make(group, shard).toString()
-      const lockNum = base + shard
-      lockNumbers.set(shardId, lockNum)
-      lockNumbersReverse.set(lockNum, shardId)
-    }
-  }
-
   const shardIdsIndex = new Map<string, number>()
   const lockNames = new Map<string, string>()
   const lockNamesReverse = new Map<string, string>()
@@ -419,11 +409,22 @@ export const make = Effect.fnUntraced(function*(options: {
     }
   }
 
-  const pgLocks = (shardIdsMap: Map<number, string>) =>
-    Array.from(
-      shardIdsMap.entries(),
-      ([lockNum, shardId]) => `pg_try_advisory_lock(${lockNum}) AS "${shardId}"`
-    ).join(", ")
+  const pgLockSeed = 1337
+  const pgLockKey = (shardId: string) => `hashtextextended(${wrapString(shardId)}, ${pgLockSeed})`
+  const pgLockExists = (shardId: string, pid: number | "pg_backend_pid()") =>
+    `EXISTS (
+      SELECT 1 FROM pg_locks
+      WHERE locktype = 'advisory'
+        AND granted = true
+        AND pid = ${pid}
+        AND ((classid::bigint << 32) | objid::bigint) = ${pgLockKey(shardId)}
+    )`
+
+  const pgLocks = (shardIds: ReadonlySet<string>) =>
+    Array.from(shardIds, (shardId) => `pg_try_advisory_lock(${pgLockKey(shardId)}) AS "${shardId}"`).join(", ")
+
+  const pgHeldLocks = (shardIds: ReadonlyArray<string>, pid: number) =>
+    shardIds.map((shardId) => `${pgLockExists(shardId, pid)} AS "${shardId}"`).join(", ")
 
   const mysqlLocks = (shardIds: ReadonlyArray<string>) =>
     shardIds.map((shardId) => `GET_LOCK('${lockNames.get(shardId)!}', 0) AS "${shardId}"`).join(", ")
@@ -551,12 +552,11 @@ export const make = Effect.fnUntraced(function*(options: {
         }
         return Effect.fnUntraced(
           function*(_address, shardId) {
-            const lockNum = lockNumbers.get(shardId)!
             for (let i = 0; i < 5; i++) {
               const [conn] = yield* lockConn!.await
-              yield* conn.executeRaw(`SELECT pg_advisory_unlock(${lockNum})`, [])
+              yield* conn.executeRaw(`SELECT pg_advisory_unlock(${pgLockKey(shardId)})`, [])
               const takenLocks = yield* conn.executeValues(
-                `SELECT 1 FROM pg_locks WHERE locktype = 'advisory' AND granted = true AND pid = pg_backend_pid() AND objid = ${lockNum}`,
+                `SELECT 1 WHERE ${pgLockExists(shardId, "pg_backend_pid()")}`,
                 []
               )
               if (takenLocks.length === 0) return
diff --git a/packages/platform-node/test/cluster/SqlRunnerStorage.test.ts b/packages/platform-node/test/cluster/SqlRunnerStorage.test.ts
index 913899875e..52a1fbe223 100644
--- a/packages/platform-node/test/cluster/SqlRunnerStorage.test.ts
+++ b/packages/platform-node/test/cluster/SqlRunnerStorage.test.ts
@@ -1,7 +1,7 @@
 import { NodeFileSystem } from "@effect/platform-node"
 import { SqliteClient } from "@effect/sql-sqlite-node"
-import { describe, expect, it } from "@effect/vitest"
-import { Effect, FileSystem, Layer } from "effect"
+import { assert, describe, expect, it } from "@effect/vitest"
+import { Context, Effect, FileSystem, Layer } from "effect"
 import {
   Runner,
   RunnerAddress,
@@ -88,9 +88,42 @@ describe("SqlRunnerStorage", () => {
         }))
     })
   })
+
+  it.effect("pg advisory locks do not collide across shard groups", () =>
+    Effect.scoped(Effect.gen(function*() {
+      const memoMap = yield* Layer.makeMemoMap
+      const scope = yield* Effect.scope
+      const pgLayer = Layer.orDie(PgContainer.layerClient)
+      const alphaLayer = StorageLive.pipe(
+        Layer.provideMerge(pgLayer),
+        Layer.provide(ShardingConfig.layer({
+          shardGroups: ["alpha"],
+          shardsPerGroup: 1
+        }))
+      )
+      const bravoLayer = StorageLive.pipe(
+        Layer.provideMerge(pgLayer),
+        Layer.provide(ShardingConfig.layer({
+          shardGroups: ["bravo"],
+          shardsPerGroup: 1
+        }))
+      )
+
+      const alphaContext = yield* Layer.buildWithMemoMap(alphaLayer, memoMap, scope)
+      const bravoContext = yield* Layer.buildWithMemoMap(bravoLayer, memoMap, scope)
+      const alphaStorage = Context.get(alphaContext, RunnerStorage.RunnerStorage)
+      const bravoStorage = Context.get(bravoContext, RunnerStorage.RunnerStorage)
+
+      const alphaAcquired = yield* alphaStorage.acquire(runnerAddress1, [ShardId.make("alpha", 1)])
+      const bravoAcquired = yield* bravoStorage.acquire(runnerAddress2, [ShardId.make("bravo", 1)])
+
+      assert.deepStrictEqual(alphaAcquired.map((_) => _.toString()), ["alpha:1"])
+      assert.deepStrictEqual(bravoAcquired.map((_) => _.toString()), ["bravo:1"])
+    })))
 })
 
 const runnerAddress1 = RunnerAddress.make("localhost", 1234)
+const runnerAddress2 = RunnerAddress.make("localhost", 1235)
 
 const SqliteLayer = Effect.gen(function*() {
   const fs = yield* FileSystem.FileSystem