diff --git a/README.md b/README.md
index 1c27cd6..b597b79 100644
--- a/README.md
+++ b/README.md
@@ -61,6 +61,7 @@ When using the transport, the following options can be used to configure the tra
 * `loggerName`: name to be used by the OpenTelemetry logger
 * `serviceVersion`: version to be used by the OpenTelemetry logger
 * `messageKey`: The key of the log message to be used as the OpenTelemetry log entry Body. Optional, value `msg` used by default (like in Pino itself). Optional
+* `severityNumberMap`: Object mapping Pino log level numbers to OpenTelemetry log severity numbers. This is an override for adding custom log levels and changing default log levels. Undefined default Pino log levels will still be mapped to their default OpenTelemetry log severity. Optional
 * `resourceAttributes`: Object containing [resource attributes](https://opentelemetry.io/docs/instrumentation/js/resources/). Optional
 * `logRecordProcessorOptions`: a single object or an array of objects specifying the LogProcessor and LogExporter types and constructor params. Optional
 
diff --git a/lib/opentelemetry-mapper.js b/lib/opentelemetry-mapper.js
index d59b55c..71bb2ad 100644
--- a/lib/opentelemetry-mapper.js
+++ b/lib/opentelemetry-mapper.js
@@ -1,23 +1,22 @@
 'use strict'
 
-const { SeverityNumber } = require('@opentelemetry/api-logs') // TODO: optional import
-
 /**
  * If the source format has only a single severity that matches the meaning of the range
  * then it is recommended to assign that severity the smallest value of the range.
  * https://github.com/open-telemetry/opentelemetry-specification/blob/fc8289b8879f3a37e1eba5b4e445c94e74b20359/specification/logs/data-model.md#mapping-of-severitynumber
  */
-const SEVERITY_NUMBER_MAP = {
-  10: SeverityNumber.TRACE,
-  20: SeverityNumber.DEBUG,
-  30: SeverityNumber.INFO,
-  40: SeverityNumber.WARN,
-  50: SeverityNumber.ERROR,
-  60: SeverityNumber.FATAL
+const DEFAULT_SEVERITY_NUMBER_MAP = {
+  10: 1, // TRACE
+  20: 5, // DEBUG
+  30: 9, // INFO
+  40: 13, // WARN
+  50: 17, // ERROR
+  60: 21 // FATAL
 }
 
 // https://github.com/open-telemetry/opentelemetry-specification/blob/fc8289b8879f3a37e1eba5b4e445c94e74b20359/specification/logs/data-model.md#displaying-severity
 const SEVERITY_NAME_MAP = {
+  0: 'UNSPECIFIED',
   1: 'TRACE',
   2: 'TRACE2',
   3: 'TRACE3',
@@ -61,12 +60,13 @@ const SEVERITY_NAME_MAP = {
  *
  * @typedef {Object} MapperOptions
  * @property {string} messageKey
+ * @property {Object.<number, number>} [severityNumberMap]
  *
  * @param {Bindings} sourceObject
  * @param {MapperOptions} mapperOptions
  * @returns {import('@opentelemetry/api-logs').LogRecord}
  */
-function toOpenTelemetry (sourceObject, { messageKey }) {
+function toOpenTelemetry (sourceObject, { messageKey, severityNumberMap = {} }) {
   const {
     time,
     level,
@@ -77,7 +77,7 @@ function toOpenTelemetry (sourceObject, { messageKey }) {
   } = sourceObject
 
   const severityNumber =
-    SEVERITY_NUMBER_MAP[sourceObject.level] ?? SeverityNumber.UNSPECIFIED
+    severityNumberMap[sourceObject.level] ?? DEFAULT_SEVERITY_NUMBER_MAP[sourceObject.level] ?? 0
   const severityText = SEVERITY_NAME_MAP[severityNumber] ?? 'UNSPECIFIED'
 
   /* eslint-disable camelcase */
diff --git a/lib/pino-opentelemetry-transport.js b/lib/pino-opentelemetry-transport.js
index 63d5d9e..ace6d5e 100644
--- a/lib/pino-opentelemetry-transport.js
+++ b/lib/pino-opentelemetry-transport.js
@@ -10,16 +10,18 @@ const DEFAULT_MESSAGE_KEY = 'msg'
  *
  * @typedef {Object} PinoOptions
  * @property {string} [messageKey="msg"]
+ * @property {Object.<number, number>} [severityNumberMap]
  *
  * @typedef {PinoOptions & import('otlp-logger').Options} Options
  *
  * @param { Options } opts
  */
-module.exports = async function (opts) {
-  const logger = getOtlpLogger(opts)
+module.exports = async function ({ messageKey = DEFAULT_MESSAGE_KEY, severityNumberMap, ...loggerOpts }) {
+  const logger = getOtlpLogger(loggerOpts)
 
   const mapperOptions = {
-    messageKey: opts.messageKey || DEFAULT_MESSAGE_KEY
+    messageKey,
+    severityNumberMap
   }
 
   return build(
diff --git a/package.json b/package.json
index 05449b1..548a7a9 100644
--- a/package.json
+++ b/package.json
@@ -16,7 +16,6 @@
   "repository": "github:Vunovati/pino-opentelemetry-transport",
   "license": "MIT",
   "dependencies": {
-    "@opentelemetry/api-logs": "^0.48.0",
     "otlp-logger": "^1.1.0",
     "pino-abstract-transport": "^1.1.0"
   },
diff --git a/test/lib/opentelemetry-mapper.test.js b/test/lib/opentelemetry-mapper.test.js
index d6b0b64..c9bea06 100644
--- a/test/lib/opentelemetry-mapper.test.js
+++ b/test/lib/opentelemetry-mapper.test.js
@@ -104,7 +104,12 @@ test('toOpenTelemetry maps all log levels correctly', async ({ match }) => {
         ...testLogEntryBase,
         level: 60
       },
-      { messageKey: 'msg' }
+      {
+        messageKey: 'msg',
+        severityNumberMap: {
+          35: 10
+        }
+      }
     ),
     {
       severityNumber: 21,
@@ -112,13 +117,37 @@ test('toOpenTelemetry maps all log levels correctly', async ({ match }) => {
     }
   )
 
+  match(
+    toOpenTelemetry(
+      {
+        ...testLogEntryBase,
+        level: 35
+      },
+      {
+        messageKey: 'msg',
+        severityNumberMap: {
+          35: 10
+        }
+      }
+    ),
+    {
+      severityNumber: 10,
+      severityText: 'INFO2'
+    }
+  )
+
   match(
     toOpenTelemetry(
       {
         ...testLogEntryBase,
         level: 42
       },
-      { messageKey: 'msg' }
+      {
+        messageKey: 'msg',
+        severityNumberMap: {
+          35: 10
+        }
+      }
     ),
     {
       severityNumber: 0,
diff --git a/test/lib/pino-opentelemetry-transport.test.js b/test/lib/pino-opentelemetry-transport.test.js
index 7513d77..91ad4b6 100644
--- a/test/lib/pino-opentelemetry-transport.test.js
+++ b/test/lib/pino-opentelemetry-transport.test.js
@@ -55,7 +55,6 @@ test('translate Pino log format to Open Telemetry data format for each log level
   })
 
   const transport = pino.transport({
-    level: 'trace',
     target: '../..',
     options: {
       loggerName: 'test-logger-name',
@@ -69,12 +68,19 @@ test('translate Pino log format to Open Telemetry data format for each log level
         exporterOptions: {
           protocol: 'grpc'
         }
+      },
+      severityNumberMap: {
+        35: 10
       }
     }
   })
 
-  const logger = pino(transport, {})
-  logger.level = 'trace'
+  const logger = pino({
+    level: 'trace',
+    customLevels: {
+      custom: 35
+    }
+  }, transport)
 
   const testTraceId = '12345678901234567890123456789012'
   const testSpanId = '1234567890123456'
@@ -93,6 +99,7 @@ test('translate Pino log format to Open Telemetry data format for each log level
   logger.trace(extra, 'test trace')
   logger.debug('test debug')
   logger.info('test info')
+  logger.custom('test custom')
   logger.warn('test warn')
   logger.error('test error')
   logger.fatal('test fatal')
@@ -143,6 +150,13 @@ test('translate Pino log format to Open Telemetry data format for each log level
       traceId: '',
       spanId: ''
     },
+    {
+      severityNumber: 10,
+      severityText: 'INFO2',
+      body: { stringValue: 'test custom' },
+      traceId: '',
+      spanId: ''
+    },
     {
       severityNumber: 13,
       severityText: 'WARN',