diff --git a/src/x86/cpu-regs.h b/src/x86/cpu-regs.h
index 3ad012bc..6c2cf4f8 100644
--- a/src/x86/cpu-regs.h
+++ b/src/x86/cpu-regs.h
@@ -32,7 +32,9 @@
 #   error not ready
 #else
 #   define SZ_PTR           4
+#   define _XSP             %esp        /* x86 stack pointer       */
 #   define _XAX             %eax        /* scratch                 */
+#   define _XBX             %ebx        /* scratch2                */
 #   define XY_Reg_X         %ebx        /* 6502 X&Y flags          */
 #   define AF_Reg_X         %ecx        /* 6502 F&A flags          */
 #   define SP_Reg_X         %edx        /* 6502 Stack pointer      */
diff --git a/src/x86/cpu.S b/src/x86/cpu.S
index 732d2c36..abcc112f 100644
--- a/src/x86/cpu.S
+++ b/src/x86/cpu.S
@@ -82,7 +82,7 @@
 
 #define BranchXCycles \
                 incb    DebugCycleCount; /* +1 branch taken */ \
-                shll    $16, %ebx; \
+                shll    $16, _XBX; \
                 movw    PC_Reg, %bx; \
                 cbw; \
                 addw    %bx, %ax; \
@@ -90,7 +90,7 @@
                 cmpb    %ah, %bh; \
                 je      9f; \
                 incb    DebugCycleCount; /* +1 branch new page */ \
-9:              shrl    $16, %ebx;
+9:              shrl    $16, _XBX;
 
 #define FlagC   lahf; \
                 andb    $C_Flag, %ah; \
@@ -2047,20 +2047,16 @@ E(cpu65_run)
                 jmp     continue1
 
 1:              movb    $0, SN(emul_reinitialize)
-                /* Zero all registers, as well as the unused 32-bit parts
-                 * of variables. (which may need to be kept 0)
-                 *
-                 * Note: dependent on assignment of registers
-                 */
+                // Zero all used registers
                 xorl    _XAX, _XAX
-                xorl    %ebx, %ebx
-                xorl    %ecx, %ecx
-                xorl    %esi, %esi
-                xorl    %edi, %edi
+                xorl    XY_Reg_X, XY_Reg_X
+                xorl    AF_Reg_X, AF_Reg_X
+                xorl    PC_Reg_X, PC_Reg_X
+                xorl    EffectiveAddr_X, EffectiveAddr_X
                 movl    $0x1FF, SP_Reg_X
                 jmp     ex_reset
 
-exit_cpu65_run:                                             // Return to timing loop ...
+exit_cpu65_run:
                 // Save CPU state when returning from being called from C
                 xorl    _XAX, _XAX
                 movw    EffectiveAddr, DebugCurrEA
@@ -2075,7 +2071,7 @@ exit_cpu65_run:                                             // Return to timing
                 popal
                 ret
 
-emul_reinit:    movb    $0, SN(cpu65__signal)               // Return to timing loop ...
+emul_reinit:    movb    $0, SN(cpu65__signal)
                 movb    $1, SN(emul_reinitialize)
                 popal
                 ret
@@ -2085,11 +2081,10 @@ emul_reinit:    movb    $0, SN(cpu65__signal)               // Return to timing
    ------------------------------------------------------------------------- */
 
 E(cpu65_direct_write)
-                /* NB: dependent on register choices */
-                pushl   %edi
-                movl    8(%esp),%edi
-                movl    12(%esp),_XAX
+                pushl   EffectiveAddr_X
+                movl    8(_XSP),EffectiveAddr_X
+                movl    12(_XSP),_XAX
                 call    *SN(cpu65_vmem)+4(,EffectiveAddr_X,SZ_PTR*2)
-                popl    %edi
+                popl    EffectiveAddr_X
                 ret
 
diff --git a/src/x86/glue-prologue.h b/src/x86/glue-prologue.h
index b69c4700..3a57d0a5 100644
--- a/src/x86/glue-prologue.h
+++ b/src/x86/glue-prologue.h
@@ -68,8 +68,8 @@ E(func)                 pushl   _XAX; \
                         pushl   _XAX; \
                         pushl   EffectiveAddr_X; \
                         call    SN(c_##func); \
-                        popl    %edx; /* dummy */ \
-                        popl    %edx; /* dummy */ \
+                        popl    EffectiveAddr_X; /* dummy */ \
+                        popl    _XAX; /* dummy */ \
                         popl    PC_Reg_X; \
                         popl    SP_Reg_X; \
                         popl    AF_Reg_X; \
@@ -86,7 +86,7 @@ E(func)                 pushl   XY_Reg_X; \
                         pushl   _XAX; /* HACK: works around mysterious issue with generated mov(_XAX), _XAX ... */ \
                         pushl   EffectiveAddr_X; \
                         call    SN(c_##func); \
-                        popl    %edx; /* dummy */ \
+                        popl    EffectiveAddr_X; /* dummy */ \
                         movb    %al, %dl; \
                         popl    _XAX; /* ... ugh */ \
                         movb    %dl, %al; \