diff --git a/sdk/xtdk/amd64/ketypes.h b/sdk/xtdk/amd64/ketypes.h
index e4eb649..fa0f6cb 100644
--- a/sdk/xtdk/amd64/ketypes.h
+++ b/sdk/xtdk/amd64/ketypes.h
@@ -183,6 +183,9 @@
 #define KTRAP_FRAME_ALIGN                 0x10
 #define KTRAP_FRAME_SIZE                  sizeof(KTRAP_FRAME)
 
+/* Initial stack reservation size */
+#define KTHREAD_STACK_INITIAL_RESERVE     ((sizeof(KTHREAD_INIT_FRAME) + STACK_ALIGNMENT - 1) & ~(STACK_ALIGNMENT - 1))
+
 /* Return address size pushed by 'call' instruction */
 #define KRETURN_ADDRESS_SIZE              0x8
 
diff --git a/sdk/xtdk/i686/ketypes.h b/sdk/xtdk/i686/ketypes.h
index 5a7fd47..6712e48 100644
--- a/sdk/xtdk/i686/ketypes.h
+++ b/sdk/xtdk/i686/ketypes.h
@@ -201,6 +201,9 @@
 #define KTRAP_FRAME_SIZE                  sizeof(KTRAP_FRAME)
 #define NPX_FRAME_SIZE                    0x210
 
+/* Initial stack reservation size */
+#define KTHREAD_STACK_INITIAL_RESERVE     ((sizeof(KTHREAD_INIT_FRAME) + STACK_ALIGNMENT - 1) & ~(STACK_ALIGNMENT - 1))
+
 /* Number of supported extensions */
 #define MAXIMUM_SUPPORTED_EXTENSION       512
 
diff --git a/xtoskrnl/ke/amd64/krnlinit.cc b/xtoskrnl/ke/amd64/krnlinit.cc
index dc5a097..4e5ee1d 100644
--- a/xtoskrnl/ke/amd64/krnlinit.cc
+++ b/xtoskrnl/ke/amd64/krnlinit.cc
@@ -213,7 +213,6 @@ KE::KernelInit::SwitchBootStack(VOID)
                      :
                      : [Stack] "r" (Stack),
                        [TargetRoutine] "r" (StartKernel),
-                       [TotalSize] "i" (FLOATING_SAVE_AREA_SIZE + KEXCEPTION_FRAME_SIZE +
-                                        KSWITCH_FRAME_SIZE + KRETURN_ADDRESS_SIZE)
+                       [TotalSize] "i" (KTHREAD_STACK_INITIAL_RESERVE)
                      : "memory", "rbp", "rsp");
 }
diff --git a/xtoskrnl/ke/i686/krnlinit.cc b/xtoskrnl/ke/i686/krnlinit.cc
index 652602a..3fb3710 100644
--- a/xtoskrnl/ke/i686/krnlinit.cc
+++ b/xtoskrnl/ke/i686/krnlinit.cc
@@ -215,6 +215,6 @@ KE::KernelInit::SwitchBootStack(VOID)
                      : [Cr0Value] "i" (CR0_EM | CR0_MP | CR0_TS),
                        [Stack] "r" (Stack),
                        [TargetRoutine] "r" (StartKernel),
-                       [TotalSize] "i" (KTRAP_FRAME_ALIGN + KTRAP_FRAME_SIZE + NPX_FRAME_SIZE + KRETURN_ADDRESS_SIZE)
+                       [TotalSize] "i" (KTHREAD_STACK_INITIAL_RESERVE)
                      : "ebp", "esp", "memory");
 }