diff --git a/markets-migrate.mjs b/markets-migrate.mjs
index 9d04dff..22f1db3 100644
--- a/markets-migrate.mjs
+++ b/markets-migrate.mjs
@@ -3,6 +3,7 @@ import process from "node:process"
 import { Client } from "pg"
 
 const databaseUrl = process.env.DATABASE_URL?.trim()
+const LEGACY_SSL_MODES = new Set(["prefer", "require", "verify-ca"])
 const MARKET_STORAGE_SCHEMA_SQL = `
 CREATE TABLE IF NOT EXISTS symbol_directory (
   symbol text PRIMARY KEY,
@@ -151,13 +152,41 @@ ALTER TABLE IF EXISTS portfolio_holdings
 DROP CONSTRAINT IF EXISTS "portfolio_holdings_userId_fkey";
 `
 
+function normalizeDatabaseConnectionString(connectionString) {
+  const normalizedConnectionString = connectionString.trim()
+  if (!normalizedConnectionString) {
+    return normalizedConnectionString
+  }
+
+  let connectionUrl
+
+  try {
+    connectionUrl = new URL(normalizedConnectionString)
+  } catch {
+    return normalizedConnectionString
+  }
+
+  const useLibpqCompat = connectionUrl.searchParams.get("uselibpqcompat")
+  if (useLibpqCompat?.toLowerCase() === "true") {
+    return normalizedConnectionString
+  }
+
+  const sslMode = connectionUrl.searchParams.get("sslmode")?.toLowerCase()
+  if (!sslMode || !LEGACY_SSL_MODES.has(sslMode)) {
+    return normalizedConnectionString
+  }
+
+  connectionUrl.searchParams.set("sslmode", "verify-full")
+  return connectionUrl.toString()
+}
+
 if (!databaseUrl) {
   console.error("Missing DATABASE_URL.")
   process.exit(1)
 }
 
 const client = new Client({
-  connectionString: databaseUrl,
+  connectionString: normalizeDatabaseConnectionString(databaseUrl),
 })
 
 await client.connect()
diff --git a/src/lib/server/__tests__/postgres.test.ts b/src/lib/server/__tests__/postgres.test.ts
new file mode 100644
index 0000000..9c2006e
--- /dev/null
+++ b/src/lib/server/__tests__/postgres.test.ts
@@ -0,0 +1,43 @@
+import { describe, expect, it } from "vitest"
+
+import { normalizeDatabaseConnectionString } from "../postgres"
+
+describe("normalizeDatabaseConnectionString", () => {
+  it("upgrades legacy sslmode=require to verify-full", () => {
+    expect(
+      normalizeDatabaseConnectionString(
+        "postgresql://user:pass@example.com/db?sslmode=require"
+      )
+    ).toBe(
+      "postgresql://user:pass@example.com/db?sslmode=verify-full"
+    )
+  })
+
+  it("keeps connection strings with explicit libpq compatibility", () => {
+    expect(
+      normalizeDatabaseConnectionString(
+        "postgresql://user:pass@example.com/db?uselibpqcompat=true&sslmode=require"
+      )
+    ).toBe(
+      "postgresql://user:pass@example.com/db?uselibpqcompat=true&sslmode=require"
+    )
+  })
+
+  it("leaves non-legacy sslmode values unchanged", () => {
+    expect(
+      normalizeDatabaseConnectionString(
+        "postgresql://user:pass@example.com/db?sslmode=verify-full"
+      )
+    ).toBe(
+      "postgresql://user:pass@example.com/db?sslmode=verify-full"
+    )
+  })
+
+  it("leaves connection strings without sslmode unchanged", () => {
+    expect(
+      normalizeDatabaseConnectionString(
+        "postgresql://user:pass@example.com/db"
+      )
+    ).toBe("postgresql://user:pass@example.com/db")
+  })
+})
diff --git a/src/lib/server/postgres.ts b/src/lib/server/postgres.ts
index 819f046..3d060ba 100644
--- a/src/lib/server/postgres.ts
+++ b/src/lib/server/postgres.ts
@@ -15,6 +15,8 @@ type DatabaseUrlEnvName =
   | typeof DATABASE_URL_ENV_NAME
   | typeof AUTH_DATABASE_URL_ENV_NAME
 
+const LEGACY_SSL_MODES = new Set(["prefer", "require", "verify-ca"])
+
 function getConfiguredDatabaseUrl(name: DatabaseUrlEnvName): string | null {
   const databaseUrl = process.env[name]?.trim()
   if (!databaseUrl) {
@@ -38,9 +40,41 @@ function getRequiredDatabaseUrl(name: DatabaseUrlEnvName): string {
   return databaseUrl
 }
 
+export function normalizeDatabaseConnectionString(
+  connectionString: string
+): string {
+  const normalizedConnectionString = connectionString.trim()
+  if (!normalizedConnectionString) {
+    return normalizedConnectionString
+  }
+
+  let connectionUrl: URL
+
+  try {
+    connectionUrl = new URL(normalizedConnectionString)
+  } catch {
+    return normalizedConnectionString
+  }
+
+  const useLibpqCompat = connectionUrl.searchParams.get("uselibpqcompat")
+  if (useLibpqCompat?.toLowerCase() === "true") {
+    return normalizedConnectionString
+  }
+
+  const sslMode = connectionUrl.searchParams.get("sslmode")?.toLowerCase()
+  if (!sslMode || !LEGACY_SSL_MODES.has(sslMode)) {
+    return normalizedConnectionString
+  }
+
+  // pg currently treats these legacy modes as verify-full. Make that explicit
+  // so builds and migrations keep the same behavior without the warning.
+  connectionUrl.searchParams.set("sslmode", "verify-full")
+  return connectionUrl.toString()
+}
+
 function createPool(connectionString: string) {
   return new Pool({
-    connectionString,
+    connectionString: normalizeDatabaseConnectionString(connectionString),
   })
 }
 
diff --git a/threads-migrate.mjs b/threads-migrate.mjs
index fad556a..0974c77 100644
--- a/threads-migrate.mjs
+++ b/threads-migrate.mjs
@@ -3,6 +3,7 @@ import process from "node:process"
 import { Client } from "pg"
 
 const databaseUrl = process.env.DATABASE_URL?.trim()
+const LEGACY_SSL_MODES = new Set(["prefer", "require", "verify-ca"])
 const THREAD_STORAGE_SCHEMA_SQL = `
 CREATE TABLE IF NOT EXISTS thread (
   "userId" text NOT NULL,
@@ -32,13 +33,41 @@ ALTER TABLE IF EXISTS thread
 DROP CONSTRAINT IF EXISTS "thread_userId_fkey";
 `
 
+function normalizeDatabaseConnectionString(connectionString) {
+  const normalizedConnectionString = connectionString.trim()
+  if (!normalizedConnectionString) {
+    return normalizedConnectionString
+  }
+
+  let connectionUrl
+
+  try {
+    connectionUrl = new URL(normalizedConnectionString)
+  } catch {
+    return normalizedConnectionString
+  }
+
+  const useLibpqCompat = connectionUrl.searchParams.get("uselibpqcompat")
+  if (useLibpqCompat?.toLowerCase() === "true") {
+    return normalizedConnectionString
+  }
+
+  const sslMode = connectionUrl.searchParams.get("sslmode")?.toLowerCase()
+  if (!sslMode || !LEGACY_SSL_MODES.has(sslMode)) {
+    return normalizedConnectionString
+  }
+
+  connectionUrl.searchParams.set("sslmode", "verify-full")
+  return connectionUrl.toString()
+}
+
 if (!databaseUrl) {
   console.error("Missing DATABASE_URL.")
   process.exit(1)
 }
 
 const client = new Client({
-  connectionString: databaseUrl,
+  connectionString: normalizeDatabaseConnectionString(databaseUrl),
 })
 
 await client.connect()