diff --git a/utils/build.ps1 b/utils/build.ps1
index 3039bfb6dfcc1..a97a504c1b3d8 100644
--- a/utils/build.ps1
+++ b/utils/build.ps1
@@ -2576,7 +2576,8 @@ function Test-Foundation {
       -Src $SourceCache\swift-corelibs-foundation `
       -Bin "$BinaryCache\$($BuildPlatform.Triple)\FoundationTests" `
       -Platform $BuildPlatform `
-      -Configuration $FoundationTestConfiguration
+      -Configuration $FoundationTestConfiguration `
+      -j 1
   }
 }