diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 966baf9ee2b..fc3e1ca096a 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -21,6 +21,9 @@ variables:
     value: .NETCore
   - name: VisualStudioDropName
     value: Products/$(System.TeamProject)/$(Build.Repository.Name)/$(Build.SourceBranchName)/$(Build.BuildNumber)
+  - ${{ if and(eq(variables['System.TeamProject'], 'public'), eq(variables['Build.Reason'], 'PullRequest')) }}:
+    - name: RunningAsPullRequest
+      value: true
 
 # Variables defined in yml cannot be overridden at queue time; instead overridable variables must be defined in the web UI.
 # Commenting out until something like this is supported: https://github.com/Microsoft/azure-pipelines-yaml/pull/129
diff --git a/eng/Build.ps1 b/eng/Build.ps1
index a7825b4d4fe..0445711695a 100644
--- a/eng/Build.ps1
+++ b/eng/Build.ps1
@@ -256,6 +256,10 @@ function TestUsingNUnit([string] $testProject, [string] $targetFramework) {
         $args += " --no-build"
     }
 
+    if ($env:RunningAsPullRequest -ne "true") {
+        $args += " --filter TestCategory!=PullRequest"
+    }
+
     Exec-Console $dotnetExe $args
 }
 
diff --git a/eng/build.sh b/eng/build.sh
index 994263ff7dd..a862cb9f385 100755
--- a/eng/build.sh
+++ b/eng/build.sh
@@ -181,10 +181,15 @@ function TestUsingNUnit() {
     exit 1
   fi
 
+  filterArgs=""
+  if [[ "${RunningAsPullRequest:-}" != "true" ]]; then
+    filterArgs=" --filter TestCategory!=PullRequest"
+  fi
+
   projectname=$(basename -- "$testproject")
   projectname="${projectname%.*}"
   testlogpath="$artifacts_dir/TestResults/$configuration/${projectname}_$targetframework.xml"
-  args="test \"$testproject\" --no-restore --no-build -c $configuration -f $targetframework --test-adapter-path . --logger \"nunit;LogFilePath=$testlogpath\""
+  args="test \"$testproject\" --no-restore --no-build -c $configuration -f $targetframework --test-adapter-path . --logger \"nunit;LogFilePath=$testlogpath\"$filterArgs"
   "$DOTNET_INSTALL_DIR/dotnet" $args || exit $?
 }
 
diff --git a/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/MailboxProcessorType.fs b/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/MailboxProcessorType.fs
index 5dfafab8770..f1bb9363113 100644
--- a/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/MailboxProcessorType.fs
+++ b/tests/FSharp.Core.UnitTests/FSharp.Core/Microsoft.FSharp.Control/MailboxProcessorType.fs
@@ -70,6 +70,7 @@ type MailboxProcessorType() =
         ()
 
     [<Test>]
+    [<Category("PullRequest")>]
     member this.``Receive handles cancellation token``() =
         let result = ref None
 
@@ -103,6 +104,7 @@ type MailboxProcessorType() =
         Assert.AreEqual(Some("Received 1 Disposed"), !result)
 
     [<Test>]
+    [<Category("PullRequest")>]
     member this.``Receive with timeout argument handles cancellation token``() =
         let result = ref None