diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 1d90e474c..05bc5b66b 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -56,6 +56,13 @@ jobs:
       PGTESTNOSSL: 'true'
       SCRAM_TEST_PGUSER: scram_test
       SCRAM_TEST_PGPASSWORD: test4scram
+      SCRAM_TEST_PGUSER_UNICODE: scram_unicode_test
+      # Raw form of a password whose NFKC normalization differs from itself.
+      # U+2168 (ROMAN NUMERAL IX) decomposes to ASCII "IX" under NFKC; the
+      # server stores the verifier from the SASLprep-normalized form, so the
+      # client must apply SASLprep too. This is the regression check for the
+      # RFC 4013 fix in packages/pg/lib/crypto/sasl.js.
+      SCRAM_TEST_PGPASSWORD_UNICODE: "IX-\u2168"
     steps:
       - name: Show OS
         run: |
@@ -63,7 +70,8 @@ jobs:
       - run: |
           psql \
             -c "SET password_encryption = 'scram-sha-256'" \
-            -c "CREATE ROLE scram_test LOGIN PASSWORD 'test4scram'"
+            -c "CREATE ROLE scram_test LOGIN PASSWORD 'test4scram'" \
+            -c "CREATE ROLE scram_unicode_test LOGIN PASSWORD U&'IX-\2168'"
       - uses: actions/checkout@v4
         with:
           persist-credentials: false
diff --git a/packages/pg/lib/crypto/sasl.js b/packages/pg/lib/crypto/sasl.js
index 47b77610c..b0d07868c 100644
--- a/packages/pg/lib/crypto/sasl.js
+++ b/packages/pg/lib/crypto/sasl.js
@@ -2,6 +2,34 @@
 const crypto = require('./utils')
 const { signatureAlgorithmHashFromCertificate } = require('./cert-signatures')
 
+// SASLprep (RFC 4013) — minimal in-tree implementation.
+//
+// Per RFC 5802 §2.2, the SCRAM-SHA-256 client must normalize the password via
+// SASLprep before feeding it into PBKDF2. PostgreSQL's server applies the same
+// SASLprep when computing the stored verifier, and libpq does the same client
+// side, so passwords whose NFKC form differs from the raw form
+// would otherwise authenticate against psql/libpq but fail against pg with `28P01`.
+//
+// We deliberately implement only the three steps that change the byte content:
+//   1. RFC 3454 Table C.1.2 (non-ASCII space) → U+0020 SPACE.
+//   2. RFC 3454 Table B.1 (commonly mapped to nothing) → empty.
+//   3. NFKC normalization.
+// We skip the prohibition (RFC 4013 §2.3) and bidi (RFC 3454 §6) checks.
+// libpq is forgiving on those paths and Postgres's own SASLprep matches that
+// leniency for legacy roles, so omitting the rejection logic keeps existing
+// roles working without adding complexity.
+function saslprep(password) {
+  // RFC 3454 Table C.1.2 — non-ASCII space characters, mapped to U+0020.
+  const nonAsciiSpace = /[\u00A0\u1680\u2000-\u200B\u202F\u205F\u3000]/g
+  // RFC 3454 Table B.1 — "commonly mapped to nothing". The set intentionally
+  // contains zero-width joiners and variation selectors — the very characters
+  // ESLint's no-misleading-character-class warns about — because they combine
+  // with their neighbors and the RFC strips them for that reason.
+  // eslint-disable-next-line no-misleading-character-class
+  const mappedToNothing = /[\u00AD\u034F\u1806\u180B\u180C\u180D\u200C\u200D\u2060\uFE00-\uFE0F\uFEFF]/g
+  return password.replace(nonAsciiSpace, ' ').replace(mappedToNothing, '').normalize('NFKC')
+}
+
 function startSession(mechanisms, stream) {
   const candidates = ['SCRAM-SHA-256']
   if (stream) candidates.unshift('SCRAM-SHA-256-PLUS') // higher-priority, so placed first
@@ -70,7 +98,7 @@ async function continueSession(session, password, serverData, stream) {
   const authMessage = clientFirstMessageBare + ',' + serverFirstMessage + ',' + clientFinalMessageWithoutProof
 
   const saltBytes = Buffer.from(sv.salt, 'base64')
-  const saltedPassword = await crypto.deriveKey(password, saltBytes, sv.iteration)
+  const saltedPassword = await crypto.deriveKey(saslprep(password), saltBytes, sv.iteration)
   const clientKey = await crypto.hmacSha256(saltedPassword, 'Client Key')
   const storedKey = await crypto.sha256(clientKey)
   const clientSignature = await crypto.hmacSha256(storedKey, authMessage)
diff --git a/packages/pg/test/integration/client/sasl-scram-tests.js b/packages/pg/test/integration/client/sasl-scram-tests.js
index 85bf2cd34..bf1dfcb0d 100644
--- a/packages/pg/test/integration/client/sasl-scram-tests.js
+++ b/packages/pg/test/integration/client/sasl-scram-tests.js
@@ -108,3 +108,82 @@ suite.test('sasl/scram fails when password is empty', async () => {
   )
   assert.ok(usingSasl, 'Should be using SASL for authentication')
 })
+
+/**
+ * SASLprep regression coverage. RFC 5802 / RFC 4013 require the SCRAM client
+ * to normalize the password (B.1 mapping → NFKC → prohibition + bidi check)
+ * before feeding it into PBKDF2. PostgreSQL's server applies the same
+ * SASLprep when computing the verifier, so any password whose NFKC form
+ * differs from the raw form would otherwise authenticate against psql/libpq
+ * but fail against pg with `28P01`.
+ *
+ * To exercise these tests, provision a role whose password contains an
+ * NFKC-asymmetric character. For example, in psql:
+ *
+ *     SET password_encryption = 'scram-sha-256';
+ *     CREATE ROLE scram_unicode_test LOGIN PASSWORD U&'IX-\2168';
+ *
+ * `\2168` is ROMAN NUMERAL IX; the server SASLprep-normalizes this to
+ * `IX-IX` when computing the verifier. Then export:
+ *
+ *     SCRAM_TEST_PGUSER_UNICODE=scram_unicode_test
+ *     SCRAM_TEST_PGPASSWORD_UNICODE='IX-\u2168'   (i.e. the raw form)
+ *
+ * If either env var is unset the suite is skipped, matching the convention
+ * of the ASCII SCRAM block above.
+ */
+const unicodeConfig = {
+  user: process.env.SCRAM_TEST_PGUSER_UNICODE,
+  password: process.env.SCRAM_TEST_PGPASSWORD_UNICODE,
+  host: process.env.SCRAM_TEST_PGHOST,
+  port: process.env.SCRAM_TEST_PGPORT,
+  database: process.env.SCRAM_TEST_PGDATABASE,
+}
+
+if (!unicodeConfig.user || !unicodeConfig.password) {
+  suite.test('skipping SCRAM unicode tests (missing env)', () => {})
+} else {
+  suite.test('sasl/scram authenticates a password requiring SASLprep (raw form)', async () => {
+    const client = new pg.Client(unicodeConfig)
+    let usingSasl = false
+    client.connection.once('authenticationSASL', () => {
+      usingSasl = true
+    })
+    await client.connect()
+    assert.ok(usingSasl, 'Should be using SASL for authentication')
+    await client.end()
+  })
+
+  suite.test('sasl/scram authenticates the NFKC-equivalent ASCII form of the same password', async () => {
+    // The unicode password contains a codepoint that NFKC-decomposes to ASCII
+    // (e.g. U+2168 → "IX"). The server stored the verifier from the
+    // SASLprep'd ASCII form, so feeding the client the ASCII form directly
+    // must also authenticate. This proves that the prep step is symmetric:
+    // any NFKC-equivalent representation reaches the same PBKDF2 input.
+    const client = new pg.Client({
+      ...unicodeConfig,
+      password: unicodeConfig.password.normalize('NFKC'),
+    })
+    await client.connect()
+    await client.end()
+  })
+
+  suite.test('sasl/scram fails when unicode password is wrong', async () => {
+    const client = new pg.Client({
+      ...unicodeConfig,
+      password: unicodeConfig.password + 'append-something-to-make-it-bad',
+    })
+    let usingSasl = false
+    client.connection.once('authenticationSASL', () => {
+      usingSasl = true
+    })
+    await assert.rejects(
+      () => client.connect(),
+      {
+        code: '28P01',
+      },
+      'Error code should be for a password error'
+    )
+    assert.ok(usingSasl, 'Should be using SASL for authentication')
+  })
+}
diff --git a/packages/pg/test/unit/client/sasl-scram-tests.js b/packages/pg/test/unit/client/sasl-scram-tests.js
index 2df0f1860..832c20d8b 100644
--- a/packages/pg/test/unit/client/sasl-scram-tests.js
+++ b/packages/pg/test/unit/client/sasl-scram-tests.js
@@ -204,6 +204,64 @@ suite.test('sasl/scram', function () {
       assert.equal(session.response, 'c=eSws,r=ab,p=YVTEOwOD7khu/NulscjFegHrZoTXJBFI/7L61AN9khc=')
     })
 
+    suite.test('SASLprep maps non-ASCII space characters (RFC 3454 C.1.2) to U+0020 SPACE', async function () {
+      // SASLprep probably misuses the C.1.2 table; U+200B, in particular, is listed in both the C.1.2 and B.1 tables. We treat it as a space for compatibility with PostgreSQL.
+      const sessionPrepped = { message: 'SASLInitialResponse', clientNonce: 'a' }
+      const sessionRef = { message: 'SASLInitialResponse', clientNonce: 'a' }
+
+      await sasl.continueSession(sessionPrepped, '\u200bfoo\xa0bar', 'r=ab,s=abcd,i=1')
+      await sasl.continueSession(sessionRef, ' foo bar', 'r=ab,s=abcd,i=1')
+
+      assert.equal(sessionPrepped.serverSignature, sessionRef.serverSignature)
+      assert.equal(sessionPrepped.response, sessionRef.response)
+    })
+
+    suite.test('SASLprep maps mapped-to-nothing characters before PBKDF2 (RFC 3454 B.1)', async function () {
+      // Soft hyphen U+00AD is mapped to nothing by SASLprep, so 'I\u00ADX'
+      // must produce identical SCRAM output to 'IX'. This proves the prep
+      // step is engaged on the SCRAM derivation path. Without the fix the
+      // two would diverge and this assertion would fail.
+      const sessionPrepped = { message: 'SASLInitialResponse', clientNonce: 'a' }
+      const sessionRef = { message: 'SASLInitialResponse', clientNonce: 'a' }
+
+      await sasl.continueSession(sessionPrepped, 'I\u00ADX', 'r=ab,s=abcd,i=1')
+      await sasl.continueSession(sessionRef, 'IX', 'r=ab,s=abcd,i=1')
+
+      assert.equal(sessionPrepped.serverSignature, sessionRef.serverSignature)
+      assert.equal(sessionPrepped.response, sessionRef.response)
+    })
+
+    suite.test('SASLprep NFKC-normalizes passwords before PBKDF2 (RFC 4013 §2.2)', async function () {
+      // ROMAN NUMERAL IX (U+2168) NFKC-decomposes to the ASCII letters 'IX'.
+      // PostgreSQL's server applies SASLprep when computing the verifier, so
+      // a role created with U+2168 is stored as if it were 'IX'. The client
+      // must do the same.
+      const sessionPrepped = { message: 'SASLInitialResponse', clientNonce: 'a' }
+      const sessionRef = { message: 'SASLInitialResponse', clientNonce: 'a' }
+
+      await sasl.continueSession(sessionPrepped, '\u2168', 'r=ab,s=abcd,i=1')
+      await sasl.continueSession(sessionRef, 'IX', 'r=ab,s=abcd,i=1')
+
+      assert.equal(sessionPrepped.serverSignature, sessionRef.serverSignature)
+      assert.equal(sessionPrepped.response, sessionRef.response)
+    })
+
+    suite.test('passes ASCII control characters through normalization unchanged', async function () {
+      // BEL (U+0007) is an ASCII control character. The minimal SASLprep
+      // implementation (B.1 mapping → C.1.2 mapping → NFKC) is the identity
+      // on ASCII control codes, so the bytes fed to PBKDF2 are exactly the
+      // raw password. We snapshot the resulting SCRAM output as a regression
+      // guard: if anyone ever swaps the order of operations, removes the
+      // NFKC step, or accidentally strips ASCII bytes, this assertion trips.
+      const session = { message: 'SASLInitialResponse', clientNonce: 'a' }
+
+      await sasl.continueSession(session, '\u0007abc', 'r=ab,s=abcd,i=1')
+
+      assert.equal(session.message, 'SASLResponse')
+      assert.equal(session.serverSignature, 'ytJN8GA+9TeZpeS28ix+u0cwaIB7iFlWgpAsmy+MmP0=')
+      assert.equal(session.response, 'c=biws,r=ab,p=04HAPnY4K2UhwiD2RJtFw9sU81SLcas8B1Uqdqv8SeQ=')
+    })
+
     suite.test('sets expected session data (SCRAM-SHA-256-PLUS)', async function () {
       const session = {
         message: 'SASLInitialResponse',