diff --git a/src/coreclr/pal/inc/unixasmmacrosamd64.inc b/src/coreclr/pal/inc/unixasmmacrosamd64.inc
index bc6d770a51824..6c4371e92f693 100644
--- a/src/coreclr/pal/inc/unixasmmacrosamd64.inc
+++ b/src/coreclr/pal/inc/unixasmmacrosamd64.inc
@@ -186,6 +186,7 @@ C_FUNC(\Name\()_End):
 
 .macro PUSH_ARGUMENT_REGISTERS
 
+        push_argument_register rax
         push_argument_register r9
         push_argument_register r8
         push_argument_register rcx
@@ -217,6 +218,7 @@ C_FUNC(\Name\()_End):
         pop_argument_register rcx
         pop_argument_register r8
         pop_argument_register r9
+        pop_argument_register rax
 
 .endm
 
@@ -257,6 +259,7 @@ C_FUNC(\Name\()_End):
 // CalleeSavedRegisters::r14
 // CalleeSavedRegisters::r13
 // CalleeSavedRegisters::r12
+// TransitionBlock::m_raxSwiftRetBufReg
 // ArgumentRegisters::r9
 // ArgumentRegisters::r8
 // ArgumentRegisters::rcx
@@ -283,7 +286,7 @@ C_FUNC(\Name\()_End):
         __PWTB_FloatArgumentRegisters = __PWTB_FloatArgumentRegisters + 8
         .endif
 
-        __PWTB_StackAlloc = __PWTB_FloatArgumentRegisters + 8 * 16 + 8 // 8 floating point registers
+        __PWTB_StackAlloc = __PWTB_FloatArgumentRegisters + 8 * 16 // 8 floating point registers
         __PWTB_TransitionBlock = __PWTB_StackAlloc
 
         .if \stackAllocOnEntry >= 4*8
diff --git a/src/coreclr/vm/amd64/theprestubamd64.S b/src/coreclr/vm/amd64/theprestubamd64.S
index dd02f70780e2f..0adfc8aab2558 100644
--- a/src/coreclr/vm/amd64/theprestubamd64.S
+++ b/src/coreclr/vm/amd64/theprestubamd64.S
@@ -14,9 +14,10 @@ NESTED_ENTRY ThePreStub, _TEXT, NoHandler
         lea             rdi, [rsp + __PWTB_TransitionBlock]     // pTransitionBlock*
         mov             rsi, METHODDESC_REGISTER
         call            C_FUNC(PreStubWorker)
+        mov             r10, rax
 
         EPILOG_WITH_TRANSITION_BLOCK_TAILCALL
-        TAILJMP_RAX
+        jmp             r10
 
 NESTED_END ThePreStub, _TEXT
 
diff --git a/src/coreclr/vm/amd64/umthunkstub.S b/src/coreclr/vm/amd64/umthunkstub.S
index 2abbbd222446c..ad5100ff84edf 100644
--- a/src/coreclr/vm/amd64/umthunkstub.S
+++ b/src/coreclr/vm/amd64/umthunkstub.S
@@ -10,8 +10,7 @@
 //
 NESTED_ENTRY TheUMEntryPrestub, _TEXT, UnhandledExceptionHandlerUnix
     PUSH_ARGUMENT_REGISTERS
-    // +8 for alignment
-    alloc_stack (SIZEOF_MAX_FP_ARG_SPILL + 8)
+    alloc_stack (SIZEOF_MAX_FP_ARG_SPILL)
     SAVE_FLOAT_ARGUMENT_REGISTERS 0
     END_PROLOGUE
 
@@ -21,7 +20,7 @@ NESTED_ENTRY TheUMEntryPrestub, _TEXT, UnhandledExceptionHandlerUnix
     // we're going to tail call to the exec stub that we just setup
 
     RESTORE_FLOAT_ARGUMENT_REGISTERS 0
-    free_stack (SIZEOF_MAX_FP_ARG_SPILL + 8)
+    free_stack (SIZEOF_MAX_FP_ARG_SPILL)
     POP_ARGUMENT_REGISTERS
     TAILJMP_RAX
 
diff --git a/src/coreclr/vm/amd64/unixasmhelpers.S b/src/coreclr/vm/amd64/unixasmhelpers.S
index 77fe1384dcd9e..7c340d159d4bb 100644
--- a/src/coreclr/vm/amd64/unixasmhelpers.S
+++ b/src/coreclr/vm/amd64/unixasmhelpers.S
@@ -75,7 +75,6 @@ NESTED_ENTRY NDirectImportThunk, _TEXT, NoHandler
         //
         PUSH_ARGUMENT_REGISTERS
         push_register r11
-        push_register rax
 
         //
         // Allocate space for XMM parameter registers and alignment
@@ -103,7 +102,6 @@ NESTED_ENTRY NDirectImportThunk, _TEXT, NoHandler
         //
         // Restore integer parameter registers, r11 and rax
         //
-        pop_register rax
         pop_register r11
         POP_ARGUMENT_REGISTERS
 
diff --git a/src/coreclr/vm/callingconvention.h b/src/coreclr/vm/callingconvention.h
index 12b935996b1a4..1ae564c0d5b73 100644
--- a/src/coreclr/vm/callingconvention.h
+++ b/src/coreclr/vm/callingconvention.h
@@ -118,6 +118,7 @@ struct TransitionBlock
 #elif defined(TARGET_AMD64)
 #ifdef UNIX_AMD64_ABI
     ArgumentRegisters       m_argumentRegisters;
+    INT64                   m_raxSwiftRetBufReg;
 #endif
     CalleeSavedRegisters    m_calleeSavedRegisters;
     TADDR                   m_ReturnAddress;