diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 90e48b4363..fba408e7d4 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -256,13 +256,16 @@ stages:
       displayName: Preserve cache diagnostics and clean failed seed outputs
       condition: and(always(), ne(variables['MSBuildCacheBuildSucceeded'], 'true'))
 
+    # Keep the cache support packages out of the multithreaded fallback. Their unannotated
+    # ResolveFileAccesses task currently fails in MSBuild's sidecar task host under -mt.
     - script: eng\common\CIBuild.cmd
         -configuration $(_BuildConfig)
+        -msbuildMultiThreaded 1
         -prepareMachine
         /p:Publish=false
         /p:Test=false
         /p:FastAcceptanceTest=true
-        /p:MSBuildCachePackageEnabled=true
+        /p:MSBuildCachePackageEnabled=false
         /p:MSBuildCacheEnabled=false
       name: Build
       displayName: Build
@@ -705,13 +708,16 @@ stages:
 
         # Fallback build. Skipped when the MSBuildCache steps above already produced, signed and packed the
         # outputs; also skipped when they failed with build errors, because this step would only reproduce them.
+        # Keep the cache support packages out of this multithreaded build because their unannotated
+        # ResolveFileAccesses task currently fails in MSBuild's sidecar task host under -mt.
         - script: eng\common\CIBuild.cmd
             -configuration $(_BuildConfig)
+            -msbuildMultiThreaded 1
             -prepareMachine
             /p:Publish=false
             /p:Test=false
             /p:FastAcceptanceTest=true
-            /p:MSBuildCachePackageEnabled=true
+            /p:MSBuildCachePackageEnabled=false
             /p:MSBuildCacheEnabled=false
           name: Build
           displayName: Build
@@ -850,6 +856,7 @@ stages:
         steps:
         - script: eng/common/cibuild.sh
             -configuration $(_BuildConfig)
+            -msbuildMultiThreaded true
             -prepareMachine
             /p:Test=false
             /p:Publish=false
@@ -889,6 +896,7 @@ stages:
         steps:
         - script: eng/common/cibuild.sh
             -configuration $(_BuildConfig)
+            -msbuildMultiThreaded true
             -prepareMachine
             /p:Test=false
             /p:Publish=false
diff --git a/eng/build.ps1 b/eng/build.ps1
index 8b80f374df..51251795b6 100644
--- a/eng/build.ps1
+++ b/eng/build.ps1
@@ -7,6 +7,7 @@ Param(
   [string] $msbuildEngine = $null,
   [bool] $warnAsError = $true,
   [bool] $nodeReuse = $true,
+  [bool][Alias('mt')]$msbuildMultiThreaded = $false,
   [switch][Alias('r')]$restore,
   [switch] $deployDeps,
   [switch][Alias('b')]$build,
@@ -82,4 +83,8 @@ if ($installWindowsSdk) {
 $null = $PSBoundParameters.Remove("vs")
 $null = $PSBoundParameters.Remove("installWindowsSdk")
 
+if (-not $PSBoundParameters.ContainsKey("msbuildMultiThreaded")) {
+    $PSBoundParameters["msbuildMultiThreaded"] = -not $ci
+}
+
 & $PSScriptRoot\common\Build.ps1 @PSBoundParameters