diff --git a/src/error/normalize/main.js b/src/error/normalize/main.js
index 622840ea..962e4201 100644
--- a/src/error/normalize/main.js
+++ b/src/error/normalize/main.js
@@ -1,3 +1,5 @@
+import { setFullStack, getStackHeader, fixStack } from './stack.js'
+
 // Ensure we are using an Error instance
 export const normalizeError = function (error) {
   if (!(error instanceof Error)) {
@@ -12,6 +14,8 @@ export const normalizeError = function (error) {
   return error
 }
 
+// If an exception is not an Error instance, create one.
+// `String()` might throw due to `value.toString()`, so we handle it.
 const createError = function (value) {
   try {
     const error = new Error(String(value))
@@ -22,6 +26,7 @@ const createError = function (value) {
   }
 }
 
+// Ensure `error.name` is a string
 const normalizeName = function (error) {
   if (!isDefinedString(error.name)) {
     setErrorProperty(
@@ -34,12 +39,14 @@ const normalizeName = function (error) {
   }
 }
 
+// Ensure `error.message` is a string
 const normalizeMessage = function (error) {
   if (!isDefinedString(error.message)) {
     error.message = ''
   }
 }
 
+// Ensure `error.stack` exists and looks normal
 const normalizeStack = function (error) {
   if (!isDefinedString(error.stack)) {
     setFullStack(error)
@@ -52,76 +59,18 @@ const normalizeStack = function (error) {
   }
 }
 
-const setFullStack = function (error) {
-  error.stack = `${getStackHeader(error)}\n${getStackTrace()}`
-}
-
-const getStackHeader = function (error) {
-  return `${error.name}: ${error.message}`
-}
-
-const fixStack = function (error, header) {
-  const lines = error.stack.split('\n')
-  const index = lines.findIndex(isStackLine)
-  const linesA = index === -1 ? [getStackTrace()] : lines.slice(index)
-  error.stack = [header, ...linesA].join('\n')
-}
-
-const isStackLine = function (line) {
-  return STACK_LINE_REGEXP.test(line)
-}
-
-const STACK_LINE_REGEXP = /^\s*at\s/u
-
-const getStackTrace = function () {
-  // eslint-disable-next-line unicorn/error-message
-  const lines = new Error('').stack.split('\n')
-  const index = findInternalIndex(lines)
-  return lines.slice(index).join('\n')
-}
-
-// Remove stack lines due to this library itself.
-// `index` should never be `-1`, but we include this as a failsafe.
-// The stack trace might be truncated, e.g. due to `Error.stackTraceLimit` in
-// Node.js, leading to the whole stack to be removed. In that case, we keep the
-// last stack line.
-const findInternalIndex = function (lines) {
-  const index = findLastIndex(lines, isInternalStackLine)
-
-  if (index === -1) {
-    return 1
-  }
-
-  return lines.length - 1 === index ? index : index + 1
-}
-
-// TODO: use `Array.findLastIndex()` after dropping support for Node <18
-const findLastIndex = function (array, condition) {
-  // eslint-disable-next-line fp/no-loops, fp/no-mutation, fp/no-let
-  for (let index = array.length - 1; index >= 0; index -= 1) {
-    // eslint-disable-next-line max-depth
-    if (condition(array[index])) {
-      return index
-    }
-  }
-
-  return -1
-}
-
-const isInternalStackLine = function (line) {
-  return line.includes(`at ${normalizeError.name}`)
-}
-
 const isDefinedString = function (value) {
   return typeof value === 'string' && value !== ''
 }
 
+// Recurse over `error.cause`
 const normalizeCause = function (error) {
   if (error.cause !== undefined) {
     error.cause = normalizeError(error.cause)
   }
 }
 
+// Recurse over `error.errors`
 const normalizeAggregate = function (error) {
   if (hasAggregate(error)) {
     error.errors = error.errors.map(normalizeError)
@@ -139,6 +88,7 @@ const isErrorInstance = function (error) {
   return error instanceof Error
 }
 
+// Error properties are non-enumerable
 const setErrorProperty = function (error, propName, value) {
   // eslint-disable-next-line fp/no-mutating-methods
   Object.defineProperty(error, 'name', {
diff --git a/src/error/normalize/stack.js b/src/error/normalize/stack.js
new file mode 100644
index 00000000..cb288824
--- /dev/null
+++ b/src/error/normalize/stack.js
@@ -0,0 +1,69 @@
+// Ensure `error.stack` reflects `error.name` and `error.message`
+// Also create stack trace if missing.
+export const setFullStack = function (error) {
+  error.stack = `${getStackHeader(error)}\n${getStackTrace()}`
+}
+
+// Expected first line of `error.stack`
+export const getStackHeader = function (error) {
+  return `${error.name}: ${error.message}`
+}
+
+// Ensure `error.stack` reflects `error.name` and `error.message`
+export const fixStack = function (error, header) {
+  const lines = error.stack.split('\n')
+  const index = lines.findIndex(isStackLine)
+  const linesA = index === -1 ? [getStackTrace()] : lines.slice(index)
+  error.stack = [header, ...linesA].join('\n')
+}
+
+const isStackLine = function (line) {
+  return STACK_LINE_REGEXP.test(line)
+}
+
+const STACK_LINE_REGEXP = /^\s*at\s/u
+
+// Generate a new stack trace
+const getStackTrace = function () {
+  // eslint-disable-next-line unicorn/error-message
+  const lines = new Error('').stack.split('\n')
+  const index = findInternalIndex(lines)
+  return lines.slice(index).join('\n')
+}
+
+// Remove stack lines due to this library itself.
+// `index` should never be `-1`, but we include this as a failsafe.
+// The stack trace might be truncated, e.g. due to `Error.stackTraceLimit` in
+// Node.js, leading to the whole stack to be removed. In that case, we keep the
+// last stack line.
+const findInternalIndex = function (lines) {
+  const index = findLastIndex(lines, isInternalStackLine)
+
+  if (index === -1) {
+    return 1
+  }
+
+  return lines.length - 1 === index ? index : index + 1
+}
+
+// TODO: use `Array.findLastIndex()` after dropping support for Node <18
+const findLastIndex = function (array, condition) {
+  // eslint-disable-next-line fp/no-loops, fp/no-mutation, fp/no-let
+  for (let index = array.length - 1; index >= 0; index -= 1) {
+    // eslint-disable-next-line max-depth
+    if (condition(array[index])) {
+      return index
+    }
+  }
+
+  return -1
+}
+
+const isInternalStackLine = function (line) {
+  return line.includes(NORMALIZE_ERROR_LINE)
+}
+
+// How the top-level function appears in a stack trace.
+// Since stack traces are implementation-specific, we must be very conservative
+// and careful. Also, we must ensure transpilation does not change this.
+const NORMALIZE_ERROR_LINE = 'at normalizeError'