diff --git a/src/coreclr/src/jit/morph.cpp b/src/coreclr/src/jit/morph.cpp
index b173993d6bb550..844692cc415437 100644
--- a/src/coreclr/src/jit/morph.cpp
+++ b/src/coreclr/src/jit/morph.cpp
@@ -6774,6 +6774,12 @@ bool Compiler::fgCanFastTailCall(GenTreeCall* callee, const char** failReason)
         return false;
     }
 
+    if (callee->IsStressTailCall())
+    {
+        reportFastTailCallDecision("Fast tail calls are not performed under tail call stress");
+        return false;
+    }
+
     // Note on vararg methods:
     // If the caller is vararg method, we don't know the number of arguments passed by caller's caller.
     // But we can be sure that in-coming arg area of vararg caller would be sufficient to hold its
@@ -7226,6 +7232,14 @@ GenTree* Compiler::fgMorphPotentialTailCall(GenTreeCall* call)
     // is set. This avoids the need for iterating through all lcl vars of the current
     // method.  Right now throughout the code base we are not consistently using 'set'
     // method to set lvHasLdAddrOp and lvAddrExposed flags.
+
+    bool isImplicitOrStressTailCall = call->IsImplicitTailCall() || call->IsStressTailCall();
+    if (isImplicitOrStressTailCall && compLocallocUsed)
+    {
+        failTailCall("Localloc used");
+        return nullptr;
+    }
+
     bool hasStructParam = false;
     for (unsigned varNum = 0; varNum < lvaCount; varNum++)
     {
@@ -7235,7 +7249,7 @@ GenTree* Compiler::fgMorphPotentialTailCall(GenTreeCall* call)
         // We still must check for any struct parameters and set 'hasStructParam'
         // so that we won't transform the recursive tail call into a loop.
         //
-        if (call->IsImplicitTailCall() || call->IsStressTailCall())
+        if (isImplicitOrStressTailCall)
         {
             if (varDsc->lvHasLdAddrOp && !lvaIsImplicitByRefLocal(varNum))
             {
diff --git a/src/libraries/System.Threading.Tasks.Parallel/tests/ParallelForTests.cs b/src/libraries/System.Threading.Tasks.Parallel/tests/ParallelForTests.cs
index 583bc08f773fab..9457f8e89425cb 100644
--- a/src/libraries/System.Threading.Tasks.Parallel/tests/ParallelForTests.cs
+++ b/src/libraries/System.Threading.Tasks.Parallel/tests/ParallelForTests.cs
@@ -1061,7 +1061,7 @@ public static void TestInvokeDOPAndCancel()
             {
                 int newVal = Interlocked.Increment(ref counter);
                 if (newVal == 1) throw new Exception("some non-cancellation-related exception");
-                if (newVal == 2) cts.Cancel();
+                if (newVal >= 2) cts.Cancel();
             };
             for (int i = 0; i < numActions; i++) actions[i] = a3;
 
diff --git a/src/libraries/System.Threading.Thread/tests/ThreadTests.cs b/src/libraries/System.Threading.Thread/tests/ThreadTests.cs
index 5bc54ba6b75b60..66d8250f5fea75 100644
--- a/src/libraries/System.Threading.Thread/tests/ThreadTests.cs
+++ b/src/libraries/System.Threading.Thread/tests/ThreadTests.cs
@@ -29,8 +29,8 @@ public static class ThreadTests
         [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsThreadingSupported))]
         public static void ConstructorTest()
         {
-            const int SmallStackSizeBytes = 64 << 10; // 64 KB, currently accepted in all supported platforms, and is the PAL minimum
-            const int LargeStackSizeBytes = 16 << 20; // 16 MB
+            const int SmallStackSizeBytes = 128 << 10; // 128 KB
+            const int LargeStackSizeBytes = 16 << 20;  // 16 MB
 
             int pageSizeBytes = Environment.SystemPageSize;