diff --git a/src/coreclr/tools/Common/TypeSystem/Interop/InteropTypes.cs b/src/coreclr/tools/Common/TypeSystem/Interop/InteropTypes.cs
index e6a684ba82e10f..9b21bf91c26496 100644
--- a/src/coreclr/tools/Common/TypeSystem/Interop/InteropTypes.cs
+++ b/src/coreclr/tools/Common/TypeSystem/Interop/InteropTypes.cs
@@ -139,7 +139,7 @@ public static bool IsSystemRuntimeIntrinsicsVector64T(TypeSystemContext context,
 
         public static bool IsInt128Type(TypeSystemContext context, TypeDesc type)
         {
-            return IsCoreNamedType(context, type, "System", "Int128") || IsCoreNamedType(context, type, "System", "UInt128");
+            return type is DefType defType && defType.IsInt128OrHasInt128Fields;
         }
 
         public static bool IsSystemRuntimeIntrinsicsVector128T(TypeSystemContext context, TypeDesc type)
diff --git a/src/tests/Interop/PInvoke/Int128/Int128Native.cpp b/src/tests/Interop/PInvoke/Int128/Int128Native.cpp
index 9cd68311421632..5b7e298b1e45f7 100644
--- a/src/tests/Interop/PInvoke/Int128/Int128Native.cpp
+++ b/src/tests/Interop/PInvoke/Int128/Int128Native.cpp
@@ -50,10 +50,11 @@ extern "C" DLL_EXPORT Int128 STDMETHODCALLTYPE GetInt128(uint64_t upper, uint64_
     return result;
 }
 
-extern "C" DLL_EXPORT void STDMETHODCALLTYPE GetInt128Out(uint64_t upper, uint64_t lower, Int128* pValue)
+
+extern "C" DLL_EXPORT void STDMETHODCALLTYPE GetInt128Out(uint64_t upper, uint64_t lower, char* pValue /* This is a char*, as .NET does not currently guarantee that Int128 values are aligned */)
 {
     Int128 value = GetInt128(upper, lower);
-    *pValue = value;
+    memcpy(pValue, &value, sizeof(value)); // Perform unaligned write
 }
 
 extern "C" DLL_EXPORT uint64_t STDMETHODCALLTYPE GetInt128Lower(Int128 value)
@@ -76,7 +77,7 @@ extern "C" DLL_EXPORT uint64_t STDMETHODCALLTYPE GetInt128Lower_S(StructJustInt1
 
 extern "C" DLL_EXPORT const Int128* STDMETHODCALLTYPE GetInt128Ptr(uint64_t upper, uint64_t lower)
 {
-    GetInt128Out(upper, lower, &Int128Value);
+    GetInt128Out(upper, lower, (char*)&Int128Value);
     return &Int128Value;
 }
 
@@ -96,11 +97,13 @@ extern "C" DLL_EXPORT Int128 STDMETHODCALLTYPE AddInt128(Int128 lhs, Int128 rhs)
 }
 
 // Test that struct alignment behavior matches with the standard OS compiler
-extern "C" DLL_EXPORT void STDMETHODCALLTYPE AddStructWithInt128_ByRef(StructWithInt128 *pLhs, StructWithInt128 *pRhs)
+extern "C" DLL_EXPORT void STDMETHODCALLTYPE AddStructWithInt128_ByRef(char *pLhs, char *pRhs) /* These are char*, as .NET does not currently guarantee that Int128 values are aligned */
 {
     StructWithInt128 result = {};
-    StructWithInt128 lhs = *pLhs;
-    StructWithInt128 rhs = *pRhs;
+    StructWithInt128 lhs;
+    memcpy(&lhs, pLhs, sizeof(lhs)); // Perform unaligned read
+    StructWithInt128 rhs;
+    memcpy(&rhs, pRhs, sizeof(rhs)); // Perform unaligned read
 
     result.messUpPadding = lhs.messUpPadding;
 
@@ -112,7 +115,7 @@ extern "C" DLL_EXPORT void STDMETHODCALLTYPE AddStructWithInt128_ByRef(StructWit
     result.value.upper = lhs.value.upper + rhs.value.upper + carry;
 #endif
 
-    *pLhs = result;
+    memcpy(pLhs, &result, sizeof(result)); // Perform unaligned write
 }
 
 extern "C" DLL_EXPORT StructWithInt128 STDMETHODCALLTYPE AddStructWithInt128(StructWithInt128 lhs, StructWithInt128 rhs)
@@ -299,13 +302,15 @@ extern "C" DLL_EXPORT Int128 STDMETHODCALLTYPE AddInt128_9(int64_t dummy1, int64
 }
 
 
-extern "C" DLL_EXPORT Int128 STDMETHODCALLTYPE AddInt128s(const Int128* pValues, uint32_t count)
+extern "C" DLL_EXPORT Int128 STDMETHODCALLTYPE AddInt128s(const char* pValues /* These are char*, as .NET does not currently guarantee that Int128 values are aligned */, uint32_t count)
 {
     Int128 result = {};
 
     for (uint32_t i = 0; i < count; i++)
     {
-        result = AddInt128(result, pValues[i]);
+        Int128 input;
+        memcpy(&input, pValues + (sizeof(Int128) * i), sizeof(Int128));  // Perform unaligned read
+        result = AddInt128(result, input);
     }
 
     return result;
diff --git a/src/tests/Interop/PInvoke/Int128/UInt128Native.cpp b/src/tests/Interop/PInvoke/Int128/UInt128Native.cpp
index 6d561cf4243439..d07d9d8f5ceb32 100644
--- a/src/tests/Interop/PInvoke/Int128/UInt128Native.cpp
+++ b/src/tests/Interop/PInvoke/Int128/UInt128Native.cpp
@@ -35,15 +35,15 @@ extern "C" DLL_EXPORT UInt128 STDMETHODCALLTYPE GetUInt128(uint64_t upper, uint6
     return result;
 }
 
-extern "C" DLL_EXPORT void STDMETHODCALLTYPE GetUInt128Out(uint64_t upper, uint64_t lower, UInt128* pValue)
+extern "C" DLL_EXPORT void STDMETHODCALLTYPE GetUInt128Out(uint64_t upper, uint64_t lower, char* pValue /* This is a char*, as .NET does not currently guarantee that Int128 values are aligned */)
 {
     UInt128 value = GetUInt128(upper, lower);
-    *pValue = value;
+    memcpy(pValue, &value, sizeof(value));  // Perform unaligned write
 }
 
 extern "C" DLL_EXPORT const UInt128* STDMETHODCALLTYPE GetUInt128Ptr(uint64_t upper, uint64_t lower)
 {
-    GetUInt128Out(upper, lower, &UInt128Value);
+    GetUInt128Out(upper, lower, (char*)&UInt128Value);
     return &UInt128Value;
 }
 
@@ -62,13 +62,15 @@ extern "C" DLL_EXPORT UInt128 STDMETHODCALLTYPE AddUInt128(UInt128 lhs, UInt128
     return result;
 }
 
-extern "C" DLL_EXPORT UInt128 STDMETHODCALLTYPE AddUInt128s(const UInt128* pValues, uint32_t count)
+extern "C" DLL_EXPORT UInt128 STDMETHODCALLTYPE AddUInt128s(const char* pValues /* These are char*, as .NET does not currently guarantee that Int128 values are aligned */, uint32_t count)
 {
     UInt128 result = {};
 
     for (uint32_t i = 0; i < count; i++)
     {
-        result = AddUInt128(result, pValues[i]);
+        UInt128 input;
+        memcpy(&input, pValues + (sizeof(UInt128) * i), sizeof(UInt128));  // Perform unaligned read
+        result = AddUInt128(result, input);
     }
 
     return result;