diff --git a/src/coreclr/src/vm/comutilnative.cpp b/src/coreclr/src/vm/comutilnative.cpp
index d4afd9102cac3b76a6bd6a51980e158592403fc0..d8c73fcb7383941c485ec2adb3b9c1f656770a7a 100644
--- a/src/coreclr/src/vm/comutilnative.cpp
+++ b/src/coreclr/src/vm/comutilnative.cpp
@@ -815,6 +815,28 @@ void QCALLTYPE MemoryNative::Clear(void *dst, size_t length)
 {
     QCALL_CONTRACT;
 
+#if defined(_X86_) || defined(_AMD64_)
+    if (length > 0x100)
+    {
+        // memset ends up calling rep stosb if the hardware claims to support it efficiently. rep stosb is up to 2x slower
+        // on misaligned blocks. Workaround this issue by aligning the blocks passed to memset upfront.
+
+        *(uint64_t*)dst = 0;
+        *((uint64_t*)dst + 1) = 0;
+        *((uint64_t*)dst + 2) = 0;
+        *((uint64_t*)dst + 3) = 0;
+
+        void* end = (uint8_t*)dst + length;
+        *((uint64_t*)end - 1) = 0;
+        *((uint64_t*)end - 2) = 0;
+        *((uint64_t*)end - 3) = 0;
+        *((uint64_t*)end - 4) = 0;
+
+        dst = ALIGN_UP((uint8_t*)dst + 1, 32);
+        length = ALIGN_DOWN((uint8_t*)end - 1, 32) - (uint8_t*)dst;
+    }
+#endif
+
     memset(dst, 0, length);
 }
 
diff --git a/src/libraries/System.Private.CoreLib/src/System/SpanHelpers.cs b/src/libraries/System.Private.CoreLib/src/System/SpanHelpers.cs
index 1c32a62b3333a8ede40db4090bfa27691f9cbafe..511b85755163ed5a6c68f565211e000969ddd89c 100644
--- a/src/libraries/System.Private.CoreLib/src/System/SpanHelpers.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/SpanHelpers.cs
@@ -24,7 +24,9 @@ public static unsafe void ClearWithoutReferences(ref byte b, nuint byteLength)
                 return;
 
 #if CORECLR && (AMD64 || ARM64)
-            if (byteLength > 4096)
+            // The exact matrix on when RhZeroMemory is faster than InitBlockUnaligned is very complex. The factors to consider include
+            // type of hardware and memory aligment. This threshold was chosen as a good balance accross different configurations.
+            if (byteLength > 768)
                 goto PInvoke;
             Unsafe.InitBlockUnaligned(ref b, 0, (uint)byteLength);
             return;