diff --git a/examples/sysir/samples.janet b/examples/sysir/samples.janet
index 6b62bfc1..b236ea9e 100644
--- a/examples/sysir/samples.janet
+++ b/examples/sysir/samples.janet
@@ -57,11 +57,11 @@
 (defsys test_arrays:myvec [a:myvec b:myvec]
   (return (+ a b)))
 
-(defsys make_array:myvec []
+'(defsys make_array:myvec []
   (def vec:myvec [0 0 0 0])
   (return vec))
 
-(defsys make_mat:mymat []
+'(defsys make_mat:mymat []
   (def mat:mymat [[1 0 0 0] [0 1 0 0] [0 0 1 0] [0 0 0 1]])
   (return mat))
 
diff --git a/examples/sysir/x64.janet b/examples/sysir/x64.janet
new file mode 100644
index 00000000..da77cbc9
--- /dev/null
+++ b/examples/sysir/x64.janet
@@ -0,0 +1,25 @@
+(use ./frontend)
+
+(defn-external printf:int [fmt:pointer x:int])
+(defn-external exit:void [x:int])
+
+(defsys doloop [x:int y:int]
+  (var i:int x)
+  #(printf "i = %d\n" i)
+  (while (< i y)
+    (set i (+ 1 i))
+    (printf "i = %d\n" i))
+  (return x))
+
+(defsys _start:void []
+  (doloop 10 20)
+  (exit (the int 0))
+  (return))
+
+(defn main [& args]
+  (def [_ what] args)
+  (dump)
+  (eprint "MODE: " what)
+  (case what
+    "c" (dumpc)
+    "x64" (dumpx64)))
diff --git a/src/core/sysir_x86.c b/src/core/sysir_x86.c
index a95791b1..d91a5867 100644
--- a/src/core/sysir_x86.c
+++ b/src/core/sysir_x86.c
@@ -204,6 +204,8 @@ void assign_registers(JanetSysx64Context *ctx) {
                     /* TODO check sizing and alignment */
                     ctx->regs[i].storage = JANET_SYSREG_STACK_PARAMETER;
                     ctx->regs[i].index = (i - 6) * 8 + 16;
+                } else {
+                    assigned |= 1 << (ctx->regs[i].index);
                 }
             } else if (cc == JANET_SYS_CC_X64_WINDOWS) {
                 if (i == 0) ctx->regs[i].index = RCX;
@@ -214,6 +216,8 @@ void assign_registers(JanetSysx64Context *ctx) {
                     /* TODO check sizing and alignment */
                     ctx->regs[i].storage = JANET_SYSREG_STACK_PARAMETER;
                     ctx->regs[i].index = (i - 4) * 8 + 16;
+                } else {
+                    assigned |= 1 << (ctx->regs[i].index);
                 }
             } else {
                 janet_panic("cannot assign registers for calling convention");
@@ -457,6 +461,51 @@ static int e_mov(JanetSysx64Context *ctx, uint32_t dest, uint32_t src) {
     }
 }
 
+/*
+push rbp
+mov rbp, rsp
+sub rsp, <stack>
+*/
+static void e_fn_prefix(JanetSysx64Context *ctx, int32_t stack) {
+    if (stack >= 128) {
+        int a = stack & 0xFF;
+        int b = (stack >> 8) & 0xFF;
+        int c = (stack >> 16) & 0xFF;
+        int d = (stack >> 24) & 0xFF;
+        janet_formatb(ctx->buffer, "db 0x55, 0x48, 0x89, 0xe5, 0x48, 0x81, 0xec, 0x%.2X, 0x%.2X, 0x%2X, 0x%2X ; function prefix\n", a, b, c, d);
+    } else {
+        janet_formatb(ctx->buffer, "db 0x55, 0x48, 0x89, 0xe5, 0x48, 0x83, 0xec, 0x%.2X ; function prefix\n", stack);
+    }
+}
+
+static void e_pushreg(JanetSysx64Context *ctx, uint32_t reg) {
+    assert(reg < 16);
+    if (reg >= 8) {
+        /* Use REX prefix */
+        janet_formatb(ctx->buffer, "db 0x41, 0x%.2X ; push %s\n", 0x50 + (reg - 8), register_names[reg]);
+    } else {
+        janet_formatb(ctx->buffer, "db 0x%.2X ; push %s\n", 0x50 + reg, register_names[reg]);
+    }
+}
+
+static void e_popreg(JanetSysx64Context *ctx, uint32_t reg) {
+    assert(reg < 16);
+    if (reg >= 8) {
+        /* Use REX prefix */
+        janet_formatb(ctx->buffer, "db 0x41, 0x%.2X ; pop %s\n", 0x58 + (reg - 8), register_names[reg]);
+    } else {
+        janet_formatb(ctx->buffer, "db 0x%.2X ; pop %s\n", 0x58 + reg, register_names[reg]);
+    }
+}
+
+/*
+leave
+ret
+*/
+static void e_fn_suffix(JanetSysx64Context *ctx) {
+    janet_formatb(ctx->buffer, "db 0xc9, 0xc3 ; function suffix\n");
+}
+
 /* Assembly emission */
 
 static const char *sysemit_sizestr(x64RegKind kind) {
@@ -715,7 +764,8 @@ static void sysemit_movfromreg(JanetSysx64Context *ctx, uint32_t dest, uint32_t
 }
 
 static void sysemit_pushreg(JanetSysx64Context *ctx, uint32_t dest_reg) {
-    janet_formatb(ctx->buffer, "push %s\n", register_names[dest_reg]);
+    e_pushreg(ctx, dest_reg);
+    //janet_formatb(ctx->buffer, "push %s\n", register_names[dest_reg]);
 }
 
 /* Move a value to a register, and save the contents of the old register on fhe stack */
@@ -725,7 +775,8 @@ static void sysemit_mov_save(JanetSysx64Context *ctx, uint32_t dest_reg, uint32_
 }
 
 static void sysemit_popreg(JanetSysx64Context *ctx, uint32_t dest_reg) {
-    janet_formatb(ctx->buffer, "pop %s\n", register_names[dest_reg]);
+    e_popreg(ctx, dest_reg);
+    //janet_formatb(ctx->buffer, "pop %s\n", register_names[dest_reg]);
 }
 
 static void sysemit_threeop(JanetSysx64Context *ctx, const char *op, uint32_t dest, uint32_t lhs, uint32_t rhs) {
@@ -759,11 +810,13 @@ static void sysemit_ret(JanetSysx64Context *ctx, uint32_t arg, int has_return) {
     /* Pop in reverse order */
     for (int32_t k = 31; k >= 0; k--) {
         if (ctx->clobbered_registers & (1u << k)) {
-            janet_formatb(ctx->buffer, "pop %s\n", register_names[k]);
+            e_popreg(ctx, k);
+            //janet_formatb(ctx->buffer, "pop %s\n", register_names[k]);
         }
     }
-    janet_formatb(ctx->buffer, "leave\n");
-    janet_formatb(ctx->buffer, "ret\n");
+    e_fn_suffix(ctx);
+    //janet_formatb(ctx->buffer, "leave\n");
+    //janet_formatb(ctx->buffer, "ret\n");
 }
 
 static int sysemit_comp(JanetSysx64Context *ctx, uint32_t index,
@@ -908,8 +961,9 @@ static void sysemit_win64_call(JanetSysx64Context *ctx, JanetSysInstruction inst
     if (save_r10) sysemit_pushreg(ctx, 10);
     if (save_r11) sysemit_pushreg(ctx, 11);
     for (uint32_t argo = 4; argo < argcount; argo++) {
-        janet_formatb(buffer, "push ");
-        sysemit_operand(ctx, args[argo], "\n");
+        e_pushreg(ctx, args[argo]);
+        //janet_formatb(buffer, "push ");
+        //sysemit_operand(ctx, args[argo], "\n");
     }
     if (instruction.opcode == JANET_SYSOP_SYSCALL) {
         sysemit_movreg(ctx, RAX, instruction.call.callee);
@@ -1000,11 +1054,13 @@ void janet_sys_ir_lower_to_x64(JanetSysIRLinkage *linkage, JanetSysTarget target
         } else {
             janet_formatb(buffer, "\n_section_%d:\n", i);
         }
-        janet_formatb(buffer, "push rbp\nmov rbp, rsp\nsub rsp, %u\n", ctx.frame_size);
+        e_fn_prefix(&ctx, ctx.frame_size);
+        //janet_formatb(buffer, "push rbp\nmov rbp, rsp\nsub rsp, %u\n", ctx.frame_size);
 
         for (uint32_t k = 0; k < 32; k++) {
             if (ctx.clobbered_registers & (1u << k)) {
-                janet_formatb(buffer, "push %s\n", register_names[k]);
+                e_pushreg(&ctx, k);
+                //janet_formatb(buffer, "push %s\n", register_names[k]);
             }
         }
 
diff --git a/tools/x64.sh b/tools/x64.sh
new file mode 100755
index 00000000..2cdca3d0
--- /dev/null
+++ b/tools/x64.sh
@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+
+case "$2" in
+c)
+    rm temp.bin temp.o temp.nasm
+    valgrind build/janet "$@" > temp.c
+    gcc -nostdlib temp.c -c temp.o
+    ;;
+x64)
+    rm temp.bin temp.o temp.nasm
+    valgrind build/janet "$@" > temp.nasm
+    nasm -felf64 temp.nasm -l temp.lst -o temp.o
+    ;;
+*)
+    echo "Unknown mode $2"
+    exit
+    ;;
+esac
+
+ld -o temp.bin -dynamic-linker /lib64/ld-linux-x86-64.so.2 -lc temp.o
+valgrind ./temp.bin