diff --git a/CHANGELOG.md b/CHANGELOG.md
index de28545..fc53d26 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,19 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 
+### Fixed
+
+- [**#102**](https://github.com/psake/PowerShellBuild/issues/102)
+  `Test-PSBuildPester` no longer raises a parameter-binding error from its
+  cleanup logic when the optional `ModuleName` parameter is not supplied.
+- [**#102**](https://github.com/psake/PowerShellBuild/issues/102)
+  `Test-PSBuildPester` now respects a Pester module that is already loaded in
+  the session instead of unconditionally importing the newest installed
+  version on top of it, which crashed with a Pester.dll version conflict when
+  two Pester versions were installed side by side. When no Pester is loaded,
+  the newest installed version (5.0.0 minimum) is imported as before, and a
+  loaded Pester older than 5.0.0 now produces a clear error.
+
 ## [0.8.2] 2026-07-08
 
 ### Fixed
diff --git a/PowerShellBuild/PowerShellBuild.psm1 b/PowerShellBuild/PowerShellBuild.psm1
index 0d4e7fa..d6ebe19 100644
--- a/PowerShellBuild/PowerShellBuild.psm1
+++ b/PowerShellBuild/PowerShellBuild.psm1
@@ -27,6 +27,7 @@ FolderDoesNotExist=Folder does not exist: {0}
 PathArgumentMustBeAFolder=The Path argument must be a folder. File paths are not allowed.
 UnableToFindModuleManifest=Unable to find module manifest [{0}]. Can't import module
 PesterTestsFailed=One or more Pester tests failed
+PesterVersionNotSupported=Pester version [{0}] is loaded, but Test-PSBuildPester requires Pester 5.0.0 or newer.
 CodeCoverage=Code Coverage
 Type=Type
 CodeCoverageLessThanThreshold=Code coverage: [{0}] is [{1:p}], which is less than the threshold of [{2:p}]
diff --git a/PowerShellBuild/Public/Test-PSBuildPester.ps1 b/PowerShellBuild/Public/Test-PSBuildPester.ps1
index 5aba62c..156d837 100644
--- a/PowerShellBuild/Public/Test-PSBuildPester.ps1
+++ b/PowerShellBuild/Public/Test-PSBuildPester.ps1
@@ -67,8 +67,15 @@ function Test-PSBuildPester {
         [string]$OutputVerbosity = 'Detailed'
     )
 
-    if (-not (Get-Module -Name Pester)) {
-        Import-Module -Name Pester -ErrorAction Stop
+    # Respect an already-loaded Pester so callers can pin a specific version; importing again
+    # would load the newest installed Pester on top of it, which crashes when two Pester
+    # versions are installed side by side. Only load Pester ourselves when none is loaded.
+    $loadedPester = Get-Module -Name Pester
+    if (-not $loadedPester) {
+        $loadedPester = Import-Module -Name Pester -MinimumVersion 5.0.0 -ErrorAction Stop -PassThru
+    }
+    if ($loadedPester.Version -lt [version]'5.0.0') {
+        throw ($LocalizedData.PesterVersionNotSupported -f $loadedPester.Version)
     }
 
     try {
@@ -84,7 +91,6 @@ function Test-PSBuildPester {
 
         Push-Location -LiteralPath $Path
 
-        Import-Module Pester -MinimumVersion 5.0.0
         $configuration = [PesterConfiguration]::Default
         $configuration.Output.Verbosity = $OutputVerbosity
         $configuration.Run.PassThru = $true
@@ -142,6 +148,10 @@ function Test-PSBuildPester {
         }
     } finally {
         Pop-Location
-        Remove-Module $ModuleName -ErrorAction SilentlyContinue
+        # ModuleName is optional; Remove-Module with an empty -Name raises a parameter-binding
+        # error that -ErrorAction SilentlyContinue cannot suppress.
+        if ($ModuleName) {
+            Remove-Module -Name $ModuleName -ErrorAction SilentlyContinue
+        }
     }
 }
diff --git a/PowerShellBuild/en-US/Messages.psd1 b/PowerShellBuild/en-US/Messages.psd1
index 58aff5e..22f370d 100644
--- a/PowerShellBuild/en-US/Messages.psd1
+++ b/PowerShellBuild/en-US/Messages.psd1
@@ -14,6 +14,7 @@ FolderDoesNotExist=Folder does not exist: {0}
 PathArgumentMustBeAFolder=The Path argument must be a folder. File paths are not allowed.
 UnableToFindModuleManifest=Unable to find module manifest [{0}]. Can't import module
 PesterTestsFailed=One or more Pester tests failed
+PesterVersionNotSupported=Pester version [{0}] is loaded, but Test-PSBuildPester requires Pester 5.0.0 or newer.
 CodeCoverage=Code Coverage
 Type=Type
 CodeCoverageLessThanThreshold=Code coverage: [{0}] is [{1:p}], which is less than the threshold of [{2:p}]
diff --git a/build.ps1 b/build.ps1
index 8529de6..4237efb 100644
--- a/build.ps1
+++ b/build.ps1
@@ -42,6 +42,9 @@ if ($Bootstrap.IsPresent) {
     }
     Import-Module -Name PSDepend -Verbose:$false
     Invoke-PSDepend -Path './requirements.psd1' -Install -Import -Force -WarningAction SilentlyContinue
+    # Install-only, never imported: importing a second Pester major into this session would
+    # crash with a Pester.dll version conflict. See requirements.pester-matrix.psd1.
+    Invoke-PSDepend -Path './requirements.pester-matrix.psd1' -Install -Force -WarningAction SilentlyContinue
 }
 
 # Execute psake task(s)
diff --git a/requirements.pester-matrix.psd1 b/requirements.pester-matrix.psd1
new file mode 100644
index 0000000..cd58532
--- /dev/null
+++ b/requirements.pester-matrix.psd1
@@ -0,0 +1,18 @@
+# Install-only dependencies. The bootstrap in build.ps1 installs this file WITHOUT importing:
+# these modules exist so the Test-PSBuildPester integration tests can pin them inside
+# subprocesses, and importing a second Pester major into the bootstrap session would crash
+# with a Pester.dll version conflict against the Pester version from requirements.psd1.
+@{
+    PSDependOptions = @{
+        Target = 'CurrentUser'
+    }
+    # Newest Pester 5.x, installed side by side with the pinned 6.x so the shipped
+    # Test-PSBuildPester function is verified against both supported majors.
+    PesterLegacy    = @{
+        Name       = 'Pester'
+        Version    = '5.9.0'
+        Parameters = @{
+            SkipPublisherCheck = $true
+        }
+    }
+}
diff --git a/tests/Test-PSBuildPester.tests.ps1 b/tests/Test-PSBuildPester.tests.ps1
new file mode 100644
index 0000000..e3cc9f7
--- /dev/null
+++ b/tests/Test-PSBuildPester.tests.ps1
@@ -0,0 +1,256 @@
+# Integration tests for Test-PSBuildPester (psake/PowerShellBuild#102).
+#
+# Test-PSBuildPester wraps Invoke-Pester, so these tests are Pester-testing-Pester. Every
+# invocation runs in a Start-Job subprocess: two Pester versions cannot coexist in one session,
+# and the subprocess lets each test pin the inner Pester version independently of the outer
+# framework. The scenarios run against every installed Pester major (5.x and 6.x) to verify the
+# shipped function keeps supporting Pester 5 consumers.
+#
+# The crash fixtures are generated into $TestDrive at runtime, never checked in, so the
+# repository's own Pester run can never discover them (see #97 for the convention).
+
+BeforeDiscovery {
+    # Newest installed Pester of each supported major version. CI installs 6.x (Pester) and
+    # 5.x (PesterLegacy) via requirements.psd1; locally, absent majors simply produce fewer
+    # matrix legs.
+    $script:innerPesterVersions = @(
+        foreach ($majorVersion in 5, 6) {
+            $newestOfMajor = Get-Module -Name 'Pester' -ListAvailable |
+                Where-Object { $_.Version.Major -eq $majorVersion } |
+                Sort-Object -Property 'Version' -Descending |
+                Select-Object -First 1
+            if ($newestOfMajor) {
+                $newestOfMajor.Version.ToString()
+            }
+        }
+    )
+}
+
+Describe 'Test-PSBuildPester' {
+
+    BeforeAll {
+        $script:moduleRoot = Split-Path -Path $PSScriptRoot -Parent
+        $script:builtModulePath = [IO.Path]::Combine($script:moduleRoot, 'Output', 'PowerShellBuild')
+
+        Import-Module -Name ([IO.Path]::Combine($PSScriptRoot, 'fixtures', 'FixtureHelpers.psm1')) -Force
+
+        # Runs Test-PSBuildPester in a subprocess with a pinned inner Pester version and reports
+        # what happened. Returns an object with Threw, ErrorMessage, and the Pester version that
+        # was loaded in the subprocess after the call.
+        function script:Invoke-TestPSBuildPesterJob {
+            param(
+                [string]$InnerPesterVersion,
+                [string]$Path,
+                [hashtable]$AdditionalParameters = @{}
+            )
+
+            $job = Start-Job -ScriptBlock {
+                param($innerPesterVersion, $builtModulePath, $path, $additionalParameters)
+
+                Import-Module -Name 'Pester' -RequiredVersion $innerPesterVersion -ErrorAction Stop
+                Import-Module -Name $builtModulePath -Force -ErrorAction Stop
+
+                $testPSBuildPesterParameters = @{
+                    Path            = $path
+                    OutputVerbosity = 'None'
+                    ErrorAction     = 'Stop'
+                }
+                foreach ($key in $additionalParameters.Keys) {
+                    $testPSBuildPesterParameters[$key] = $additionalParameters[$key]
+                }
+
+                $threw = $false
+                $errorMessage = $null
+                try {
+                    Test-PSBuildPester @testPSBuildPesterParameters
+                } catch {
+                    $threw = $true
+                    $errorMessage = $_.Exception.Message
+                }
+
+                [PSCustomObject]@{
+                    Threw                = $threw
+                    ErrorMessage         = $errorMessage
+                    LoadedPesterVersions = @((Get-Module -Name 'Pester').Version.ToString())
+                }
+            } -ArgumentList $InnerPesterVersion, $script:builtModulePath, $Path, $AdditionalParameters
+
+            $jobResult = $job | Wait-Job | Receive-Job
+            Remove-Job -Job $job -Force
+            $jobResult
+        }
+
+        # Scenario directories, generated at runtime.
+        $script:healthyPath = Join-Path -Path $TestDrive -ChildPath 'healthy'
+        $script:failingTestPath = Join-Path -Path $TestDrive -ChildPath 'failingtest'
+        $script:beforeAllCrashPath = Join-Path -Path $TestDrive -ChildPath 'beforeallcrash'
+        $script:discoveryCrashPath = Join-Path -Path $TestDrive -ChildPath 'discoverycrash'
+        $script:coveragePath = Join-Path -Path $TestDrive -ChildPath 'coverage'
+        $script:outputPath = Join-Path -Path $TestDrive -ChildPath 'out'
+        foreach ($directory in @(
+                $script:healthyPath
+                $script:failingTestPath
+                $script:beforeAllCrashPath
+                $script:discoveryCrashPath
+                $script:coveragePath
+                $script:outputPath
+            )) {
+            New-Item -Path $directory -ItemType Directory -Force > $null
+        }
+
+        Set-Content -Path (Join-Path -Path $script:healthyPath -ChildPath 'Healthy.tests.ps1') -Value @'
+Describe 'Healthy suite' {
+    It 'passes' {
+        1 | Should -Be 1
+    }
+}
+'@
+
+        Set-Content -Path (Join-Path -Path $script:failingTestPath -ChildPath 'FailingTest.tests.ps1') -Value @'
+Describe 'Suite with a failing test' {
+    It 'fails' {
+        1 | Should -Be 2
+    }
+}
+'@
+
+        Set-Content -Path (Join-Path -Path $script:beforeAllCrashPath -ChildPath 'BeforeAllCrash.tests.ps1') -Value @'
+Describe 'Suite with a broken setup' {
+    BeforeAll {
+        throw 'BeforeAll exploded'
+    }
+
+    It 'never executes' {
+        1 | Should -Be 1
+    }
+}
+'@
+
+        Set-Content -Path (Join-Path -Path $script:discoveryCrashPath -ChildPath 'DiscoveryCrash.tests.ps1') -Value @'
+throw 'file exploded during discovery'
+
+Describe 'Unreachable suite' {
+    It 'is never discovered' {
+        1 | Should -Be 1
+    }
+}
+'@
+
+        # Coverage scenario: tests exercising the fixture module, with coverage measured on the
+        # fixture's public functions.
+        $script:fixturePath = Copy-PSBuildTestFixture -Destination $TestDrive
+        $fixtureManifestPath = Join-Path -Path $script:fixturePath -ChildPath 'PSBuildTestFixture.psd1'
+        Set-Content -Path (Join-Path -Path $script:coveragePath -ChildPath 'Coverage.tests.ps1') -Value @"
+BeforeAll {
+    Import-Module -Name '$fixtureManifestPath' -Force
+}
+
+Describe 'Coverage target' {
+    It 'calls Get-Widget' {
+        (Get-Widget -Name 'Sprocket').Name | Should -Be 'Sprocket'
+    }
+}
+"@
+    }
+
+    AfterAll {
+        Remove-Module -Name 'FixtureHelpers' -Force -ErrorAction SilentlyContinue
+    }
+
+    Context 'with inner Pester <_>' -ForEach $script:innerPesterVersions {
+
+        BeforeAll {
+            $script:innerVersion = $_
+        }
+
+        It 'succeeds for a healthy suite' {
+            $result = Invoke-TestPSBuildPesterJob -InnerPesterVersion $script:innerVersion -Path $script:healthyPath
+
+            $result.Threw | Should -BeFalse
+        }
+
+        It 'fails the build when a test fails' {
+            # Regression: #52
+            $result = Invoke-TestPSBuildPesterJob -InnerPesterVersion $script:innerVersion -Path $script:failingTestPath
+
+            $result.Threw | Should -BeTrue
+            $result.ErrorMessage | Should -Match 'Pester tests failed'
+        }
+
+        It 'fails the build when a setup block throws' {
+            # Regression: #128 / #133 (FailedCount alone misses failed blocks)
+            $result = Invoke-TestPSBuildPesterJob -InnerPesterVersion $script:innerVersion -Path $script:beforeAllCrashPath
+
+            $result.Threw | Should -BeTrue
+            $result.ErrorMessage | Should -Match 'Pester tests failed'
+        }
+
+        It 'fails the build when a test file errors during discovery' {
+            # Regression: #128 / #133 (FailedCount alone misses failed containers)
+            $result = Invoke-TestPSBuildPesterJob -InnerPesterVersion $script:innerVersion -Path $script:discoveryCrashPath
+
+            $result.Threw | Should -BeTrue
+            $result.ErrorMessage | Should -Match 'Pester tests failed'
+        }
+
+        It 'writes test results to the requested output path' {
+            $testResultsPath = Join-Path -Path $script:outputPath -ChildPath "testResults-$script:innerVersion.xml"
+            $additionalParameters = @{
+                OutputPath = $testResultsPath
+            }
+            $result = Invoke-TestPSBuildPesterJob -InnerPesterVersion $script:innerVersion -Path $script:healthyPath -AdditionalParameters $additionalParameters
+
+            $result.Threw | Should -BeFalse
+            $testResultsPath | Should -Exist
+        }
+
+        It 'writes code coverage in the requested format to the requested path' {
+            # Regression: #62
+            $coverageOutputPath = Join-Path -Path $script:outputPath -ChildPath "coverage-$script:innerVersion.xml"
+            $additionalParameters = @{
+                CodeCoverage                 = $true
+                CodeCoverageFiles            = @(Join-Path -Path $script:fixturePath -ChildPath 'Public/*.ps1')
+                CodeCoverageOutputFile       = $coverageOutputPath
+                CodeCoverageOutputFileFormat = 'JaCoCo'
+            }
+            $result = Invoke-TestPSBuildPesterJob -InnerPesterVersion $script:innerVersion -Path $script:coveragePath -AdditionalParameters $additionalParameters
+
+            $result.Threw | Should -BeFalse
+            $coverageOutputPath | Should -Exist
+            [xml]$coverageReport = Get-Content -Path $coverageOutputPath -Raw
+            $coverageReport.report | Should -Not -BeNullOrEmpty
+        }
+    }
+
+    # BeforeDiscovery variables are not visible during the run phase, so the discovered version
+    # list is handed to the run phase through -ForEach.
+    Context 'Regressions independent of the inner Pester version' -ForEach @(
+        @{ AvailableVersions = $script:innerPesterVersions }
+    ) {
+
+        BeforeAll {
+            $script:newestInnerVersion = $AvailableVersions | Select-Object -Last 1
+            $script:oldestInnerVersion = $AvailableVersions | Select-Object -First 1
+        }
+
+        It 'does not error when ModuleName is not provided' {
+            # Regression: the finally block called Remove-Module with an empty -Name, which
+            # raised a parameter-binding error that -ErrorAction SilentlyContinue cannot
+            # suppress.
+            $result = Invoke-TestPSBuildPesterJob -InnerPesterVersion $script:newestInnerVersion -Path $script:healthyPath
+
+            $result.Threw | Should -BeFalse
+            $result.ErrorMessage | Should -BeNullOrEmpty
+        }
+
+        It 'honors the Pester version that is already loaded' -Skip:($script:innerPesterVersions.Count -lt 2) {
+            # Regression: an unconditional Import-Module Pester -MinimumVersion 5.0.0 loaded the
+            # newest installed Pester on top of an already-loaded older one, which crashes with a
+            # Pester.dll version conflict when 5.x and 6.x are installed side by side.
+            $result = Invoke-TestPSBuildPesterJob -InnerPesterVersion $script:oldestInnerVersion -Path $script:healthyPath
+
+            $result.Threw | Should -BeFalse
+            $result.LoadedPesterVersions | Should -Be @($script:oldestInnerVersion)
+        }
+    }
+}