diff --git a/packages/pg-protocol/src/buffer-writer.ts b/packages/pg-protocol/src/buffer-writer.ts
index cebb0d9ed..d206f322a 100644
--- a/packages/pg-protocol/src/buffer-writer.ts
+++ b/packages/pg-protocol/src/buffer-writer.ts
@@ -58,6 +58,26 @@ export class Writer {
     return this
   }
 
+  // Write an Int32 byte-length prefix immediately followed by the string's UTF-8
+  // bytes. Postgres' Bind wire format prefixes every parameter with its length,
+  // and doing it in one method computes Buffer.byteLength ONCE — the previous
+  // `addInt32(Buffer.byteLength(s)).addString(s)` pairing scanned the string
+  // three times (byteLength for the prefix, byteLength again inside addString,
+  // then the encode), which is costly for large text parameters.
+  public addInt32PrefixedString(string: string): Writer {
+    const len = Buffer.byteLength(string)
+    this.ensure(4 + len)
+    const buffer = this.buffer
+    let offset = this.offset
+    buffer[offset++] = (len >>> 24) & 0xff
+    buffer[offset++] = (len >>> 16) & 0xff
+    buffer[offset++] = (len >>> 8) & 0xff
+    buffer[offset++] = (len >>> 0) & 0xff
+    buffer.write(string, offset, 'utf-8')
+    this.offset = offset + len
+    return this
+  }
+
   public add(otherBuffer: Buffer): Writer {
     this.ensure(otherBuffer.length)
     otherBuffer.copy(this.buffer, this.offset)
diff --git a/packages/pg-protocol/src/outbound-serializer.test.ts b/packages/pg-protocol/src/outbound-serializer.test.ts
index 0d3e387e4..856ead7b9 100644
--- a/packages/pg-protocol/src/outbound-serializer.test.ts
+++ b/packages/pg-protocol/src/outbound-serializer.test.ts
@@ -129,6 +129,28 @@ describe('serializer', () => {
         .join(true, 'B')
       assert.deepEqual(actual, expectedBuffer)
     })
+
+    it('encodes a multi-byte string param with its UTF-8 byte length, not char length', function () {
+      // Guards the single-pass addInt32PrefixedString write path: the Int32
+      // length prefix must be the UTF-8 byte count, not String.length. 'héllo中🎉'
+      // is 7 code points / 8 UTF-16 code units but 13 UTF-8 bytes.
+      const value = 'héllo中🎉'
+      const bytes = Buffer.from(value, 'utf8')
+      assert.notEqual(bytes.length, value.length) // sanity: the divergence we're testing
+      const actual = serialize.bind({ values: [value] })
+      const expectedBuffer = new BufferList()
+        .addCString('') // portal
+        .addCString('') // statement
+        .addInt16(1) // param format code count
+        .addInt16(0) // format code for the one value (text)
+        .addInt16(1) // value count
+        .addInt32(bytes.length) // 13 — the UTF-8 byte length, NOT value.length (8)
+        .add(bytes)
+        .addInt16(1) // result format code count
+        .addInt16(0) // result format (text)
+        .join(true, 'B')
+      assert.deepEqual(actual, expectedBuffer)
+    })
   })
 
   it('with custom valueMapper', function () {
diff --git a/packages/pg-protocol/src/serializer.ts b/packages/pg-protocol/src/serializer.ts
index bb0441f56..137daad79 100644
--- a/packages/pg-protocol/src/serializer.ts
+++ b/packages/pg-protocol/src/serializer.ts
@@ -48,7 +48,7 @@ const password = (password: string): Buffer => {
 
 const sendSASLInitialResponseMessage = function (mechanism: string, initialResponse: string): Buffer {
   // 0x70 = 'p'
-  writer.addCString(mechanism).addInt32(Buffer.byteLength(initialResponse)).addString(initialResponse)
+  writer.addCString(mechanism).addInt32PrefixedString(initialResponse)
 
   return writer.flush(code.startup)
 }
@@ -135,8 +135,8 @@ const writeValues = function (values: any[], valueMapper?: ValueMapper): void {
     } else {
       // add the param type (string) to the writer
       writer.addInt16(ParamType.STRING)
-      paramWriter.addInt32(Buffer.byteLength(mappedVal))
-      paramWriter.addString(mappedVal)
+      // length prefix + UTF-8 bytes in one pass (Buffer.byteLength computed once)
+      paramWriter.addInt32PrefixedString(mappedVal)
     }
   }
 }