diff --git a/README.md b/README.md
index 0aac54d..5a84b10 100644
--- a/README.md
+++ b/README.md
@@ -183,7 +183,7 @@ import the ones you need yourself.
 | `base64`, `base64pad`, `base64url`, `base64urlpad`            | `multiformats/bases/base64` | [multiformats/js-multiformats](https://github.com/multiformats/js-multiformats/tree/master/bases) |
 | `base58btc`, `base58flick4`                                   | `multiformats/bases/base58` | [multiformats/js-multiformats](https://github.com/multiformats/js-multiformats/tree/master/bases) |
 
-Other (less useful) bases implemented in [multiformats/js-multiformats](https://github.com/multiformats/js-multiformats/tree/master/bases) include: `base2`, `base8`, `base10`, `base36` and `base256emoji`.
+Other (less useful) bases implemented in [multiformats/js-multiformats](https://github.com/multiformats/js-multiformats/tree/master/bases) include: `base2`, `base8`, `base10`, `base36`, `base45` and `base256emoji`.
 
 ### Multihash hashers
 
diff --git a/package.json b/package.json
index c1543af..238f307 100644
--- a/package.json
+++ b/package.json
@@ -81,6 +81,11 @@
       "import": "./dist/src/bases/base36.js",
       "module-sync": "./dist/src/bases/base36.js"
     },
+    "./bases/base45": {
+      "types": "./dist/src/bases/base45.d.ts",
+      "import": "./dist/src/bases/base45.js",
+      "module-sync": "./dist/src/bases/base45.js"
+    },
     "./bases/base58": {
       "types": "./dist/src/bases/base58.d.ts",
       "import": "./dist/src/bases/base58.js",
diff --git a/src/bases/base45.ts b/src/bases/base45.ts
new file mode 100644
index 0000000..b1682c8
--- /dev/null
+++ b/src/bases/base45.ts
@@ -0,0 +1,61 @@
+import { from } from './base.ts'
+
+const alphabet = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ $%*+-./:'
+const INVALID = 0xff
+const decodeTable = (() => {
+  const table = new Uint8Array(256).fill(INVALID)
+  for (let i = 0; i < alphabet.length; i++) {
+    table[alphabet.charCodeAt(i)] = i
+  }
+  return table
+})()
+
+function decodeChar (input: string, i: number): number {
+  const v = decodeTable[input.charCodeAt(i)]
+  if (v === INVALID) {
+    throw new Error(`Non-base45 character: ${input[i]}`)
+  }
+  return v
+}
+
+export const base45 = from({
+  name: 'base45',
+  prefix: 'R',
+  encode: (input: Uint8Array): string => {
+    let ret = ''
+    for (let i = 0; i < input.length; i += 2) {
+      if (i + 1 === input.length) {
+        const v = input[i]
+        ret += alphabet[v % 45] + alphabet[(v / 45) | 0]
+        break
+      }
+      const v = (input[i] << 8) | input[i + 1]
+      ret += alphabet[v % 45] + alphabet[((v / 45) | 0) % 45] + alphabet[(v / 2025) | 0]
+    }
+    return ret
+  },
+  decode: (input: string): Uint8Array<ArrayBuffer> => {
+    if ((input.length * 2) % 3 === 2) {
+      throw new Error('Unexpected end of data')
+    }
+    const out = new Uint8Array(((input.length * 2) / 3) | 0)
+    let o = 0
+    for (let i = 0; i < input.length; i += 3) {
+      if (i + 2 === input.length) {
+        const v = decodeChar(input, i) + decodeChar(input, i + 1) * 45
+        if (v > 0xff) {
+          throw new Error('Invalid base45 encoding: trailing chunk out of range')
+        }
+        out[o++] = v
+        break
+      }
+      const v = decodeChar(input, i) + decodeChar(input, i + 1) * 45 + decodeChar(input, i + 2) * 2025
+      if (v > 0xffff) {
+        throw new Error('Invalid base45 encoding: chunk out of range')
+      }
+      out[o++] = v >> 8
+      out[o++] = v & 0xff
+    }
+    return out
+  }
+})
diff --git a/src/basics.ts b/src/basics.ts
index d4c2a55..f63d4b9 100644
--- a/src/basics.ts
+++ b/src/basics.ts
@@ -4,6 +4,7 @@ import * as base2 from './bases/base2.ts'
 import * as base256emoji from './bases/base256emoji.ts'
 import * as base32 from './bases/base32.ts'
 import * as base36 from './bases/base36.ts'
+import * as base45 from './bases/base45.ts'
 import * as base58 from './bases/base58.ts'
 import * as base64 from './bases/base64.ts'
 import * as base8 from './bases/base8.ts'
@@ -14,7 +15,7 @@ import * as identity from './hashes/identity.ts'
 import * as sha2 from './hashes/sha2.ts'
 import { CID, hasher, digest, varint, bytes } from './index.ts'
 
-export const bases = { ...identityBase, ...base2, ...base8, ...base10, ...base16, ...base32, ...base36, ...base58, ...base64, ...base256emoji }
+export const bases = { ...identityBase, ...base2, ...base8, ...base10, ...base16, ...base32, ...base36, ...base45, ...base58, ...base64, ...base256emoji }
 export const hashes = { ...sha2, ...identity }
 export const codecs = { raw, json }
 
diff --git a/src/index.ts b/src/index.ts
index 494f6a1..71acb0c 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -176,7 +176,7 @@
  * | `base64`, `base64pad`, `base64url`, `base64urlpad`            | `multiformats/bases/base64` | [multiformats/js-multiformats](https://github.com/multiformats/js-multiformats/tree/master/bases) |
  * | `base58btc`, `base58flick4`                                   | `multiformats/bases/base58` | [multiformats/js-multiformats](https://github.com/multiformats/js-multiformats/tree/master/bases) |
  *
- * Other (less useful) bases implemented in [multiformats/js-multiformats](https://github.com/multiformats/js-multiformats/tree/master/bases) include: `base2`, `base8`, `base10`, `base36` and `base256emoji`.
+ * Other (less useful) bases implemented in [multiformats/js-multiformats](https://github.com/multiformats/js-multiformats/tree/master/bases) include: `base2`, `base8`, `base10`, `base36`, `base45` and `base256emoji`.
  *
  * ### Multihash hashers
  *
diff --git a/test/test-multibase-spec.spec.ts b/test/test-multibase-spec.spec.ts
index 63d5acf..047e0b3 100644
--- a/test/test-multibase-spec.spec.ts
+++ b/test/test-multibase-spec.spec.ts
@@ -23,6 +23,7 @@ const encoded = [
       ['base32z', 'het1sg3mqqt3gn5djxj11y3msci3817depfzgqejb'],
       ['base36', 'k343ixo7d49hqj1ium15pgy1wzww5fxrid21td7l'],
       ['base36upper', 'K343IXO7D49HQJ1IUM15PGY1WZWW5FXRID21TD7L'],
+      ['base45', 'R4T8KPCG/DVKEXVDDLFD44O/EALEAWEZEDV1DX0'],
       ['base58flickr', 'Ztwe7gVTeK8wswS1gf8hrgAua9fcw9reboD'],
       ['base58btc', 'zUXE7GvtEk8XTXs1GF8HSGbVA9FCX9SEBPe'],
       ['base64', 'mRGVjZW50cmFsaXplIGV2ZXJ5dGhpbmchIQ'],
@@ -52,6 +53,7 @@ const encoded = [
       ['base32z', 'hxf1zgedpcfzg1ebb'],
       ['base36', 'k2lcpzo5yikidynfl'],
       ['base36upper', 'K2LCPZO5YIKIDYNFL'],
+      ['base45', 'RRFF.OEB$D5/DZ24'],
       ['base58flickr', 'Z7Pznk19XTTzBtx'],
       ['base58btc', 'z7paNL19xttacUY'],
       ['base64', 'meWVzIG1hbmkgIQ'],
@@ -81,6 +83,7 @@ const encoded = [
       ['base32z', 'hpb1sa5dxrb5s6hucco'],
       ['base36', 'kfuvrsivvnfrbjwajo'],
       ['base36upper', 'KFUVRSIVVNFRBJWAJO'],
+      ['base45', 'R+8D VD82EK4F.KEA2'],
       ['base58flickr', 'ZrTu1dk6cWsRYjYu'],
       ['base58btc', 'zStV1DL6CwTryKyV'],
       ['base64', 'maGVsbG8gd29ybGQ'],
@@ -110,6 +113,7 @@ const encoded = [
       ['base32z', 'hybhskh3ypiosh4jyrr'],
       ['base36', 'k02lcpzo5yikidynfl'],
       ['base36upper', 'K02LCPZO5YIKIDYNFL'],
+      ['base45', 'RV206$CL44CEC2DDX0'],
       ['base58flickr', 'Z17Pznk19XTTzBtx'],
       ['base58btc', 'z17paNL19xttacUY'],
       ['base64', 'mAHllcyBtYW5pICE'],
@@ -139,6 +143,7 @@ const encoded = [
       ['base32z', 'hyyy813murbssn5ujryoo'],
       ['base36', 'k002lcpzo5yikidynfl'],
       ['base36upper', 'K002LCPZO5YIKIDYNFL'],
+      ['base45', 'R000RFF.OEB$D5/DZ24'],
       ['base58flickr', 'Z117Pznk19XTTzBtx'],
       ['base58btc', 'z117paNL19xttacUY'],
       ['base64', 'mAAB5ZXMgbWFuaSAh'],
@@ -147,7 +152,11 @@ const encoded = [
       ['base64urlpad', 'UAAB5ZXMgbWFuaSAh'],
       ['base256emoji', '🚀🚀🚀🏃✋🌈😅🌷🤤😻🌟😅👏']
     ]
-  }
+  },
+  { input: 'AB', tests: [['base45', 'RBB8']] },
+  { input: 'Hello!!', tests: [['base45', 'R%69 VD92EX0']] },
+  { input: 'base-45', tests: [['base45', 'RUJCLQE7W581']] },
+  { input: 'ietf!', tests: [['base45', 'RQED8WEX0']] }
 ]
 
 describe('spec test', () => {
@@ -158,12 +167,12 @@ describe('spec test', () => {
         const base = bases[name as keyof typeof bases]
 
         describe(name, () => {
-          it('should encode buffer', () => {
+          it(`should encode from buffer [${input}]`, () => {
             const out = base.encode(fromString(input))
             assert.deepStrictEqual(out, output)
           })
 
-          it('should decode string', () => {
+          it(`should decode from string [${input}]`, () => {
             assert.deepStrictEqual(base.decode(output), fromString(input))
           })
         })
@@ -180,4 +189,25 @@ describe('spec test', () => {
       assert.throws(() => base.decode(base.prefix + '^!@$%!#$%@#y'), `Non-${base.name} character`)
     })
   }
+
+  it('base45 should fail with invalid input', () => {
+    // not enough input chars, should be multiple of 3 or multiple of 3 + 2
+    assert.throws(() => bases.base45.decode('R%69 VD92EX'), 'Unexpected end of data')
+  })
+
+  // RFC9285 section 6: encoded chunks must lie within the byte ranges they
+  // represent; 3-char chunks decode to a 16-bit value, 2-char trailers to 8-bit.
+  for (const input of ['RGGW', 'R:::', 'R000V5', 'R000::']) {
+    it(`base45 should fail with out-of-range encoding [${input}]`, () => {
+      assert.throws(() => bases.base45.decode(input), 'Invalid base45 encoding')
+    })
+  }
+
+  // RFC9285 section 6 boundary: "FGW" is 65535 (0xFFFF), the largest valid
+  // 16-bit value; the contrasting "GGW" (above) is 65536 and must fail.
+  it('base45 should round-trip the 0xFFFF boundary [FGW]', () => {
+    const bytes = Uint8Array.from([0xff, 0xff])
+    assert.deepStrictEqual(bases.base45.encode(bytes), 'RFGW')
+    assert.deepStrictEqual(bases.base45.decode('RFGW'), bytes)
+  })
 })
diff --git a/test/test-multibase.spec.ts b/test/test-multibase.spec.ts
index 0e00059..130131c 100644
--- a/test/test-multibase.spec.ts
+++ b/test/test-multibase.spec.ts
@@ -6,6 +6,7 @@ import * as b16 from '../src/bases/base16.ts'
 import * as b2 from '../src/bases/base2.ts'
 import * as b32 from '../src/bases/base32.ts'
 import * as b36 from '../src/bases/base36.ts'
+import * as b45 from '../src/bases/base45.ts'
 import * as b58 from '../src/bases/base58.ts'
 import * as b64 from '../src/bases/base64.ts'
 import * as b8 from '../src/bases/base8.ts'
@@ -64,7 +65,7 @@ describe('multibase', () => {
   const buff = bytes.fromString('test')
   const nonPrintableBuff = Uint8Array.from([239, 250, 254])
 
-  const baseTest = (bases: typeof b2 | typeof b8 | typeof b10 | typeof b16 | typeof b32 | typeof b36 | typeof b58 | typeof b64): void => {
+  const baseTest = (bases: typeof b2 | typeof b8 | typeof b10 | typeof b16 | typeof b32 | typeof b36 | typeof b45 | typeof b58 | typeof b64): void => {
     for (const base of Object.values(bases)) {
       if (((base as { name: string })?.name) !== '') {
         it(`encode/decode ${base.name}`, () => {
@@ -110,6 +111,10 @@ describe('multibase', () => {
     baseTest(b36)
   })
 
+  describe('base45', () => {
+    baseTest(b45)
+  })
+
   describe('base58', () => {
     baseTest(b58)
   })
diff --git a/typedoc.json b/typedoc.json
index 87e4675..688689d 100644
--- a/typedoc.json
+++ b/typedoc.json
@@ -7,6 +7,7 @@
     "./src/bases/base256emoji.ts",
     "./src/bases/base32.ts",
     "./src/bases/base36.ts",
+    "./src/bases/base45.ts",
     "./src/bases/base58.ts",
     "./src/bases/base64.ts",
     "./src/bases/base8.ts",