diff --git a/src/codegen.cpp b/src/codegen.cpp
index 110286a3c9..f60f116a2c 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -805,14 +805,12 @@ static LLVMValueRef gen_asm_expr(CodeGen *g, AstNode *node) {
     LLVMValueRef *param_values = allocate<LLVMValueRef>(input_and_output_count);
     for (int i = 0; i < asm_expr->output_list.length; i += 1, total_index += 1) {
         AsmOutput *asm_output = asm_expr->output_list.at(i);
-        bool is_return = false;
-        if (buf_eql_str(&asm_output->constraint, "=m")) {
-            buf_append_str(&constraint_buf, "=*m");
-        } else if (buf_eql_str(&asm_output->constraint, "=r")) {
-            buf_append_str(&constraint_buf, "=r");
-            is_return = true;
+        bool is_return = (asm_output->return_type != nullptr);
+        assert(*buf_ptr(&asm_output->constraint) == '=');
+        if (is_return) {
+            buf_appendf(&constraint_buf, "=%s", buf_ptr(&asm_output->constraint) + 1);
         } else {
-            zig_panic("TODO unable to handle anything other than '=m' and '=r' for outputs");
+            buf_appendf(&constraint_buf, "=*%s", buf_ptr(&asm_output->constraint) + 1);
         }
         if (total_index + 1 < total_constraint_count) {
             buf_append_char(&constraint_buf, ',');
diff --git a/std/std.zig b/std/std.zig
index d3ce4f976c..b0aa266be6 100644
--- a/std/std.zig
+++ b/std/std.zig
@@ -3,27 +3,17 @@ const SYS_exit : isize = 60;
 const stdout_fileno : isize = 1;
 
 fn syscall1(number: isize, arg1: isize) -> isize {
-    asm volatile ("
-        mov %[number], %%rax
-        mov %[arg1], %%rdi
-        syscall
-        mov %%rax, %[ret]"
-        : [ret] "=r" (return isize)
-        : [number] "r" (number), [arg1] "r" (arg1)
-        : "rcx", "r11", "rax", "rdi")
+    asm volatile ("syscall"
+        : [ret] "={rax}" (return isize)
+        : [number] "{rax}" (number), [arg1] "{rdi}" (arg1)
+        : "rcx", "r11")
 }
 
 fn syscall3(number: isize, arg1: isize, arg2: isize, arg3: isize) -> isize {
-    asm volatile ("
-        mov %[number], %%rax
-        mov %[arg1], %%rdi
-        mov %[arg2], %%rsi
-        mov %[arg3], %%rdx
-        syscall
-        mov %%rax, %[ret]"
-        : [ret] "=r" (return isize)
-        : [number] "r" (number), [arg1] "r" (arg1), [arg2] "r" (arg2), [arg3] "r" (arg3)
-        : "rcx", "r11", "rax", "rdi", "rsi", "rdx")
+    asm volatile ("syscall"
+        : [ret] "={rax}" (return isize)
+        : [number] "{rax}" (number), [arg1] "{rdi}" (arg1), [arg2] "{rsi}" (arg2), [arg3] "{rdx}" (arg3)
+        : "rcx", "r11")
 }
 
 pub fn write(fd: isize, buf: &const u8, count: usize) -> isize {