diff --git a/repos/base-hw/src/core/spec/x86_64/mode_transition.s b/repos/base-hw/src/core/spec/x86_64/mode_transition.s
index 25c57e8a6..656123dab 100644
--- a/repos/base-hw/src/core/spec/x86_64/mode_transition.s
+++ b/repos/base-hw/src/core/spec/x86_64/mode_transition.s
@@ -21,11 +21,12 @@
 .set BUFFER_SIZE, 6 * 8
 
 /* offsets of the member variables in a CPU context */
-.set SP_OFFSET,     1 * 8
-.set R8_OFFSET,     2 * 8
-.set RAX_OFFSET,   10 * 8
-.set FLAGS_OFFSET, 18 * 8
-.set CR3_OFFSET,   20 * 8
+.set SP_OFFSET,       1 * 8
+.set R8_OFFSET,       2 * 8
+.set RAX_OFFSET,     10 * 8
+.set ERRCODE_OFFSET, 17 * 8
+.set FLAGS_OFFSET,   18 * 8
+.set CR3_OFFSET,     21 * 8
 
 .section .text
 
@@ -48,7 +49,7 @@
 	_mt_master_context_begin:
 
 	/* space must be at least as large as 'Cpu_state' */
-	.space 21*8
+	.space 22*8
 
 	.global _mt_master_context_end
 	_mt_master_context_end:
diff --git a/repos/base/include/x86_64/cpu/cpu_state.h b/repos/base/include/x86_64/cpu/cpu_state.h
index 1b7eb9ef8..abe1da273 100644
--- a/repos/base/include/x86_64/cpu/cpu_state.h
+++ b/repos/base/include/x86_64/cpu/cpu_state.h
@@ -23,26 +23,27 @@ namespace Genode { struct Cpu_state; }
 
 struct Genode::Cpu_state
 {
-	addr_t ip     = 0;
-	addr_t sp     = 0;
-	addr_t r8     = 0;
-	addr_t r9     = 0;
-	addr_t r10    = 0;
-	addr_t r11    = 0;
-	addr_t r12    = 0;
-	addr_t r13    = 0;
-	addr_t r14    = 0;
-	addr_t r15    = 0;
-	addr_t rax    = 0;
-	addr_t rbx    = 0;
-	addr_t rcx    = 0;
-	addr_t rdx    = 0;
-	addr_t rdi    = 0;
-	addr_t rsi    = 0;
-	addr_t rbp    = 0;
-	addr_t ss     = 0;
-	addr_t eflags = 0;
-	addr_t trapno = 0;
+	addr_t ip      = 0;
+	addr_t sp      = 0;
+	addr_t r8      = 0;
+	addr_t r9      = 0;
+	addr_t r10     = 0;
+	addr_t r11     = 0;
+	addr_t r12     = 0;
+	addr_t r13     = 0;
+	addr_t r14     = 0;
+	addr_t r15     = 0;
+	addr_t rax     = 0;
+	addr_t rbx     = 0;
+	addr_t rcx     = 0;
+	addr_t rdx     = 0;
+	addr_t rdi     = 0;
+	addr_t rsi     = 0;
+	addr_t rbp     = 0;
+	addr_t errcode = 0;
+	addr_t eflags  = 0;
+	addr_t trapno  = 0;
+	addr_t ss      = 0;
 };
 
 #endif /* _INCLUDE__X86_64__CPU__CPU_STATE_H_ */