diff --git a/.gitignore b/.gitignore
index dea0e1b..58c8909 100644
--- a/.gitignore
+++ b/.gitignore
@@ -136,6 +136,9 @@ _TeamCity*
 *.coverage
 *.coveragexml
 
+# Pester coverage
+coverage.xml
+
 # NCrunch
 _NCrunch_*
 .*crunch*.local.xml
diff --git a/tools/run-tests.ps1 b/tools/run-tests.ps1
index 7d063ba..7f3f5d2 100644
--- a/tools/run-tests.ps1
+++ b/tools/run-tests.ps1
@@ -10,20 +10,22 @@ $testDir = Join-Path $parentDir -ChildPath "test"
 
 # Debug info.
 $PSVersionTable | Out-String
+$RequiredPesterVersion = "5.3.3"
 
-# List Pester versions.
-$pesterVersions = Get-Module -ListAvailable | Where-Object {$_.Name -eq "Pester" }
-$pesterVersions | % { Write-Host $_.Name $_.Version }
+$pesterVersions = Get-Module -ListAvailable | Where-Object {$_.Name -eq "Pester" -and $_.Version -eq $RequiredPesterVersion}
 
 if ($pesterVersions.Count -eq 0) {
-   Write-Warning "No Pester found, will install Pester 5.1.0"
+   Write-Warning "Pester $RequiredPesterVersion not found, installing it."
    $InstallPester = $true
 }
 
 if ($InstallPester) {
-   Install-Module Pester -Force -Scope CurrentUser -RequiredVersion 5.1.0
+   Install-Module Pester -Force -Scope CurrentUser -RequiredVersion $RequiredPesterVersion -SkipPublisherCheck
 }
 
+Get-Module -Name Pester | Remove-Module
+Import-Module Pester -RequiredVersion $RequiredPesterVersion
+
 $FailedTests = Invoke-Pester $testDir -EnableExit -OutputFile "test/results.xml" -OutputFormat "NUnitXML" -CodeCoverage "$parentDir/FeatureFlags.psm1"
 if ($FailedTests -gt 0) {
     Write-Error "Error: $FailedTests Pester tests failed."