diff --git a/chibicc.h b/chibicc.h
index ac145ce..7123dbd 100644
--- a/chibicc.h
+++ b/chibicc.h
@@ -146,6 +146,7 @@ struct Node {
   int64_t val;   // Used if kind == ND_NUM
 };
 
+Node *new_cast(Node *expr, Type *ty);
 Obj *parse(Token *tok);
 
 //
diff --git a/codegen.c b/codegen.c
index 31f4002..2fb7e83 100644
--- a/codegen.c
+++ b/codegen.c
@@ -81,10 +81,15 @@ static void load(Type *ty) {
     return;
   }
 
+  // When we load a char or a short value to a register, we always
+  // extend them to the size of int, so we can assume the lower half of
+  // a register always contains a valid value. The upper half of a
+  // register for char, short and int may contain garbage. When we load
+  // a long value to a register, it simply occupies the entire register.
   if (ty->size == 1)
-    println("  movsbq (%%rax), %%rax");
+    println("  movsbl (%%rax), %%eax");
   else if (ty->size == 2)
-    println("  movswq (%%rax), %%rax");
+    println("  movswl (%%rax), %%eax");
   else if (ty->size == 4)
     println("  movsxd (%%rax), %%rax");
   else
diff --git a/parse.c b/parse.c
index a36c4f6..ba29f00 100644
--- a/parse.c
+++ b/parse.c
@@ -134,13 +134,20 @@ static Node *new_num(int64_t val, Token *tok) {
   return node;
 }
 
+static Node *new_long(int64_t val, Token *tok) {
+  Node *node = new_node(ND_NUM, tok);
+  node->val = val;
+  node->ty = ty_long;
+  return node;
+}
+
 static Node *new_var_node(Obj *var, Token *tok) {
   Node *node = new_node(ND_VAR, tok);
   node->var = var;
   return node;
 }
 
-static Node *new_cast(Node *expr, Type *ty) {
+Node *new_cast(Node *expr, Type *ty) {
   add_type(expr);
 
   Node *node = calloc(1, sizeof(Node));
@@ -664,7 +671,7 @@ static Node *new_add(Node *lhs, Node *rhs, Token *tok) {
   }
 
   // ptr + num
-  rhs = new_binary(ND_MUL, rhs, new_num(lhs->ty->base->size, tok), tok);
+  rhs = new_binary(ND_MUL, rhs, new_long(lhs->ty->base->size, tok), tok);
   return new_binary(ND_ADD, lhs, rhs, tok);
 }
 
@@ -679,7 +686,7 @@ static Node *new_sub(Node *lhs, Node *rhs, Token *tok) {
 
   // ptr - num
   if (lhs->ty->base && is_integer(rhs->ty)) {
-    rhs = new_binary(ND_MUL, rhs, new_num(lhs->ty->base->size, tok), tok);
+    rhs = new_binary(ND_MUL, rhs, new_long(lhs->ty->base->size, tok), tok);
     add_type(rhs);
     Node *node = new_binary(ND_SUB, lhs, rhs, tok);
     node->ty = lhs->ty;
diff --git a/test/arith.c b/test/arith.c
index 44b699c..d116a20 100644
--- a/test/arith.c
+++ b/test/arith.c
@@ -31,6 +31,8 @@ int main() {
   ASSERT(1, 1>=1);
   ASSERT(0, 1>=2);
 
+  ASSERT(0, 1073741824 * 100 / 100);
+
   printf("OK\n");
   return 0;
 }
diff --git a/test/sizeof.c b/test/sizeof.c
index e63bd6d..da43d89 100644
--- a/test/sizeof.c
+++ b/test/sizeof.c
@@ -19,6 +19,15 @@ int main() {
   ASSERT(48, sizeof(int[3][4]));
   ASSERT(8, sizeof(struct {int a; int b;}));
 
+  ASSERT(8, sizeof(-10 + (long)5));
+  ASSERT(8, sizeof(-10 - (long)5));
+  ASSERT(8, sizeof(-10 * (long)5));
+  ASSERT(8, sizeof(-10 / (long)5));
+  ASSERT(8, sizeof((long)-10 + 5));
+  ASSERT(8, sizeof((long)-10 - 5));
+  ASSERT(8, sizeof((long)-10 * 5));
+  ASSERT(8, sizeof((long)-10 / 5));
+
   printf("OK\n");
   return 0;
 }
diff --git a/test/usualconv.c b/test/usualconv.c
new file mode 100644
index 0000000..b1f951a
--- /dev/null
+++ b/test/usualconv.c
@@ -0,0 +1,28 @@
+#include "test.h"
+
+int main() {
+  ASSERT((long)-5, -10 + (long)5);
+  ASSERT((long)-15, -10 - (long)5);
+  ASSERT((long)-50, -10 * (long)5);
+  ASSERT((long)-2, -10 / (long)5);
+
+  ASSERT(1, -2 < (long)-1);
+  ASSERT(1, -2 <= (long)-1);
+  ASSERT(0, -2 > (long)-1);
+  ASSERT(0, -2 >= (long)-1);
+
+  ASSERT(1, (long)-2 < -1);
+  ASSERT(1, (long)-2 <= -1);
+  ASSERT(0, (long)-2 > -1);
+  ASSERT(0, (long)-2 >= -1);
+
+  ASSERT(0, 2147483647 + 2147483647 + 2);
+  ASSERT((long)-1, ({ long x; x=-1; x; }));
+
+  ASSERT(1, ({ char x[3]; x[0]=0; x[1]=1; x[2]=2; char *y=x+1; y[0]; }));
+  ASSERT(0, ({ char x[3]; x[0]=0; x[1]=1; x[2]=2; char *y=x+1; y[-1]; }));
+  ASSERT(5, ({ struct t {char a;} x, y; x.a=5; y=x; y.a; }));
+
+  printf("OK\n");
+  return 0;
+}
diff --git a/type.c b/type.c
index 78f09d9..dbdb705 100644
--- a/type.c
+++ b/type.c
@@ -47,6 +47,27 @@ Type *array_of(Type *base, int len) {
   return ty;
 }
 
+static Type *get_common_type(Type *ty1, Type *ty2) {
+  if (ty1->base)
+    return pointer_to(ty1->base);
+  if (ty1->size == 8 || ty2->size == 8)
+    return ty_long;
+  return ty_int;
+}
+
+// For many binary operators, we implicitly promote operands so that
+// both operands have the same type. Any integral type smaller than
+// int is always promoted to int. If the type of one operand is larger
+// than the other's (e.g. "long" vs. "int"), the smaller operand will
+// be promoted to match with the other.
+//
+// This operation is called the "usual arithmetic conversion".
+static void usual_arith_conv(Node **lhs, Node **rhs) {
+  Type *ty = get_common_type((*lhs)->ty, (*rhs)->ty);
+  *lhs = new_cast(*lhs, ty);
+  *rhs = new_cast(*rhs, ty);
+}
+
 void add_type(Node *node) {
   if (!node || node->ty)
     return;
@@ -65,23 +86,36 @@ void add_type(Node *node) {
     add_type(n);
 
   switch (node->kind) {
+  case ND_NUM:
+    node->ty = (node->val == (int)node->val) ? ty_int : ty_long;
+    return;
   case ND_ADD:
   case ND_SUB:
   case ND_MUL:
   case ND_DIV:
-  case ND_NEG:
+    usual_arith_conv(&node->lhs, &node->rhs);
     node->ty = node->lhs->ty;
     return;
+  case ND_NEG: {
+    Type *ty = get_common_type(ty_int, node->lhs->ty);
+    node->lhs = new_cast(node->lhs, ty);
+    node->ty = ty;
+    return;
+  }
   case ND_ASSIGN:
     if (node->lhs->ty->kind == TY_ARRAY)
       error_tok(node->lhs->tok, "not an lvalue");
+    if (node->lhs->ty->kind != TY_STRUCT)
+      node->rhs = new_cast(node->rhs, node->lhs->ty);
     node->ty = node->lhs->ty;
     return;
   case ND_EQ:
   case ND_NE:
   case ND_LT:
   case ND_LE:
-  case ND_NUM:
+    usual_arith_conv(&node->lhs, &node->rhs);
+    node->ty = ty_int;
+    return;
   case ND_FUNCALL:
     node->ty = ty_long;
     return;