diff --git a/codegen.c b/codegen.c
index 8f8ca1fd309d5c59aae001a82bc43d3d47fec576..5db73abf1f0103aee05578d50ddebb244b577783 100644
--- a/codegen.c
+++ b/codegen.c
@@ -173,25 +173,38 @@ static void gen_expr(Node *node) {
   gen_expr(node->lhs);
   pop("%rdi");
 
+  char *ax, *di;
+
+  if (node->lhs->ty->kind == TY_LONG || node->lhs->ty->base) {
+    ax = "%rax";
+    di = "%rdi";
+  } else {
+    ax = "%eax";
+    di = "%edi";
+  }
+
   switch (node->kind) {
   case ND_ADD:
-    println("  add %%rdi, %%rax");
+    println("  add %s, %s", di, ax);
     return;
   case ND_SUB:
-    println("  sub %%rdi, %%rax");
+    println("  sub %s, %s", di, ax);
     return;
   case ND_MUL:
-    println("  imul %%rdi, %%rax");
+    println("  imul %s, %s", di, ax);
     return;
   case ND_DIV:
-    println("  cqo");
-    println("  idiv %%rdi");
+    if (node->lhs->ty->size == 8)
+      println("  cqo");
+    else
+      println("  cdq");
+    println("  idiv %s", di);
     return;
   case ND_EQ:
   case ND_NE:
   case ND_LT:
   case ND_LE:
-    println("  cmp %%rdi, %%rax");
+    println("  cmp %s, %s", di, ax);
 
     if (node->kind == ND_EQ)
       println("  sete %%al");