diff --git a/src/coreclr/nativeaot/Runtime/portable.cpp b/src/coreclr/nativeaot/Runtime/portable.cpp
index 2f30e42253d876..c6f83d09c1ff0d 100644
--- a/src/coreclr/nativeaot/Runtime/portable.cpp
+++ b/src/coreclr/nativeaot/Runtime/portable.cpp
@@ -127,7 +127,7 @@ FCIMPL2(Array *, RhpNewArrayFast, MethodTable * pArrayEEType, int numElements)
 }
 FCIMPLEND
 
-FCIMPL2(String *, RhNewString, MethodTable * pArrayEEType, int numElements)
+FCIMPL2(String *, RhNewString, MethodTable * pArrayEEType, intptr_t numElements)
 {
     // TODO: Implement. We tail call to RhpNewArrayFast for now since there's a bunch of TODOs in the places
     // that matter anyway.
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Runtime/RuntimeImports.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Runtime/RuntimeImports.cs
index 7adbb86c7fcd2d..e1886df7006f31 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Runtime/RuntimeImports.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Runtime/RuntimeImports.cs
@@ -396,7 +396,7 @@ internal static IntPtr RhHandleAllocDependent(object primary, object secondary)
 
         [MethodImpl(MethodImplOptions.InternalCall)]
         [RuntimeImport(RuntimeLibrary, "RhNewString")]
-        internal static extern unsafe string RhNewString(MethodTable* pEEType, int length);
+        internal static extern unsafe string RhNewString(MethodTable* pEEType, nint length);
 
         [MethodImpl(MethodImplOptions.InternalCall)]
         [RuntimeImport(RuntimeLibrary, "RhUnbox")]
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/String.NativeAot.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/String.NativeAot.cs
index a8efc76018a30d..2e951b445befe9 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/String.NativeAot.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/String.NativeAot.cs
@@ -18,7 +18,7 @@ public partial class String
         [Intrinsic]
         public static readonly string Empty = "";
 
-        internal static unsafe string FastAllocateString(int length)
+        internal static unsafe string FastAllocateString(nint length)
         {
             // We allocate one extra char as an interop convenience so that our strings are null-
             // terminated, however, we don't pass the extra +1 to the string allocation because the base
diff --git a/src/coreclr/nativeaot/Test.CoreLib/src/System/Runtime/RuntimeImports.cs b/src/coreclr/nativeaot/Test.CoreLib/src/System/Runtime/RuntimeImports.cs
index 026f0b8d109cc6..7703d63dee84a0 100644
--- a/src/coreclr/nativeaot/Test.CoreLib/src/System/Runtime/RuntimeImports.cs
+++ b/src/coreclr/nativeaot/Test.CoreLib/src/System/Runtime/RuntimeImports.cs
@@ -82,7 +82,7 @@ internal static IntPtr RhGetModuleSection(TypeManagerHandle module, ReadyToRunSe
 
         [MethodImpl(MethodImplOptions.InternalCall)]
         [RuntimeImport(RuntimeLibrary, "RhNewString")]
-        internal static extern unsafe string RhNewString(MethodTable* pEEType, int length);
+        internal static extern unsafe string RhNewString(MethodTable* pEEType, nint length);
 
         [DllImport(RuntimeLibrary)]
         internal static extern unsafe void RhAllocateNewArray(MethodTable* pArrayEEType, uint numElements, uint flags, void* pResult);
diff --git a/src/coreclr/runtime/amd64/AllocFast.S b/src/coreclr/runtime/amd64/AllocFast.S
index d5b366b876dad6..a8b6fcd5bf5053 100644
--- a/src/coreclr/runtime/amd64/AllocFast.S
+++ b/src/coreclr/runtime/amd64/AllocFast.S
@@ -173,7 +173,7 @@ NESTED_END RhpNewObject, _TEXT
 
 // Allocate a string.
 //  RDI == MethodTable
-//  ESI == character/element count
+//  RSI == character/element count
 LEAF_ENTRY RhNewString, _TEXT
 
         // we want to limit the element count to the non-negative 32-bit int range
diff --git a/src/coreclr/runtime/amd64/AllocFast.asm b/src/coreclr/runtime/amd64/AllocFast.asm
index c099cb829b2c83..cda88f3bf8f1ec 100644
--- a/src/coreclr/runtime/amd64/AllocFast.asm
+++ b/src/coreclr/runtime/amd64/AllocFast.asm
@@ -128,7 +128,7 @@ ENDM ; NEW_ARRAY_FAST
 
 ;; Allocate a string.
 ;;  RCX == MethodTable
-;;  EDX == character/element count
+;;  RDX == character/element count
 LEAF_ENTRY RhNewString, _TEXT
 
         ; we want to limit the element count to the non-negative 32-bit int range
diff --git a/src/coreclr/vm/jitinterface.h b/src/coreclr/vm/jitinterface.h
index 7116f37690d1dd..d715ab80939ac5 100644
--- a/src/coreclr/vm/jitinterface.h
+++ b/src/coreclr/vm/jitinterface.h
@@ -149,7 +149,7 @@ EXTERN_C FCDECL1(void*, JIT_GetDynamicNonGCStaticBaseNoCtor_Portable, DynamicSta
 EXTERN_C FCDECL1(Object*, RhpNewFast, CORINFO_CLASS_HANDLE typeHnd_);
 EXTERN_C FCDECL2(Object*, RhpNewArrayFast, CORINFO_CLASS_HANDLE typeHnd_, INT_PTR size);
 EXTERN_C FCDECL2(Object*, RhpNewPtrArrayFast, CORINFO_CLASS_HANDLE typeHnd_, INT_PTR size);
-EXTERN_C FCDECL2(Object*, RhNewString, CORINFO_CLASS_HANDLE typeHnd_, DWORD stringLength);
+EXTERN_C FCDECL2(Object*, RhNewString, CORINFO_CLASS_HANDLE typeHnd_, INT_PTR stringLength);
 
 #if defined(FEATURE_64BIT_ALIGNMENT)
 EXTERN_C FCDECL1(Object*, RhpNewFastAlign8, CORINFO_CLASS_HANDLE typeHnd_);
@@ -161,7 +161,7 @@ EXTERN_C FCDECL2(Object*, RhpNewArrayFastAlign8, CORINFO_CLASS_HANDLE typeHnd_,
 EXTERN_C FCDECL1(Object*, RhpNewFast_UP, CORINFO_CLASS_HANDLE typeHnd_);
 EXTERN_C FCDECL2(Object*, RhpNewArrayFast_UP, CORINFO_CLASS_HANDLE typeHnd_, INT_PTR size);
 EXTERN_C FCDECL2(Object*, RhpNewPtrArrayFast_UP, CORINFO_CLASS_HANDLE typeHnd_, INT_PTR size);
-EXTERN_C FCDECL2(Object*, RhNewString_UP, CORINFO_CLASS_HANDLE typeHnd_, DWORD stringLength);
+EXTERN_C FCDECL2(Object*, RhNewString_UP, CORINFO_CLASS_HANDLE typeHnd_, INT_PTR stringLength);
 #endif
 
 EXTERN_C FCDECL1(Object*, RhpNew, CORINFO_CLASS_HANDLE typeHnd_);
@@ -169,9 +169,6 @@ EXTERN_C FCDECL2(Object*, RhpNewVariableSizeObject, CORINFO_CLASS_HANDLE typeHnd
 EXTERN_C FCDECL1(Object*, RhpNewMaybeFrozen, CORINFO_CLASS_HANDLE typeHnd_);
 EXTERN_C FCDECL2(Object*, RhpNewArrayMaybeFrozen, CORINFO_CLASS_HANDLE typeHnd_, INT_PTR size);
 
-EXTERN_C FCDECL1(Object*, AllocateStringFast, DWORD stringLength);
-EXTERN_C FCDECL1(Object*, AllocateStringSlow, DWORD stringLength);
-
 EXTERN_C FCDECL2(void, JITutil_MonReliableEnter, Object* obj, BYTE* pbLockTaken);
 EXTERN_C FCDECL3(void, JITutil_MonTryEnter, Object* obj, INT32 timeOut, BYTE* pbLockTaken);
 EXTERN_C FCDECL2(void, JITutil_MonReliableContention, AwareLock* awarelock, BYTE* pbLockTaken);