diff --git a/chibi.h b/chibi.h
index 50d0f088..f2404ce9 100644
--- a/chibi.h
+++ b/chibi.h
@@ -109,6 +109,7 @@ typedef enum {
   ND_MEMBER,     // . (struct member access)
   ND_ADDR,       // unary &
   ND_DEREF,      // unary *
+  ND_NOT,        // !
   ND_RETURN,     // "return"
   ND_IF,         // "if"
   ND_WHILE,      // "while"
diff --git a/codegen.c b/codegen.c
index ffa88f41..6da620fb 100644
--- a/codegen.c
+++ b/codegen.c
@@ -260,6 +260,14 @@ static void gen(Node *node) {
     if (node->ty->kind != TY_ARRAY)
       load(node->ty);
     return;
+  case ND_NOT:
+    gen(node->lhs);
+    printf("  pop rax\n");
+    printf("  cmp rax, 0\n");
+    printf("  sete al\n");
+    printf("  movzb rax, al\n");
+    printf("  push rax\n");
+    return;
   case ND_IF: {
     int seq = labelseq++;
     if (node->els) {
diff --git a/examples/nqueen.c b/examples/nqueen.c
index ce847e05..281ffa75 100644
--- a/examples/nqueen.c
+++ b/examples/nqueen.c
@@ -38,8 +38,7 @@ int solve(int (*board)[10], int row) {
     return 0;
   }
   for (int i = 0; i < 10; i++) {
-    if (conflict(board, row, i)) {
-    } else {
+    if (!conflict(board, row, i)) {
       board[row][i] = 1;
       solve(board, row + 1);
       board[row][i] = 0;
diff --git a/parse.c b/parse.c
index f045e89d..715caa9d 100644
--- a/parse.c
+++ b/parse.c
@@ -885,7 +885,7 @@ static Node *cast(void) {
   return unary();
 }
 
-// unary = ("+" | "-" | "*" | "&")? cast
+// unary = ("+" | "-" | "*" | "&" | "!")? cast
 //       | ("++" | "--") unary
 //       | postfix
 static Node *unary(void) {
@@ -898,6 +898,8 @@ static Node *unary(void) {
     return new_unary(ND_ADDR, cast(), tok);
   if (tok = consume("*"))
     return new_unary(ND_DEREF, cast(), tok);
+  if (tok = consume("!"))
+    return new_unary(ND_NOT, cast(), tok);
   if (tok = consume("++"))
     return new_unary(ND_PRE_INC, unary(), tok);
   if (tok = consume("--"))
diff --git a/tests b/tests
index 8121a0d3..2d25e4e3 100644
--- a/tests
+++ b/tests
@@ -390,6 +390,10 @@ int main() {
   assert(47, 0b101111, "0b101111");
   assert(47, 0B101111, "0B101111");
 
+  assert(0, !1, "!1");
+  assert(0, !2, "!2");
+  assert(1, !0, "!0");
+
   printf("OK\n");
   return 0;
 }
diff --git a/type.c b/type.c
index 0bfcd9fd..fe69ec2f 100644
--- a/type.c
+++ b/type.c
@@ -76,6 +76,7 @@ void add_type(Node *node) {
   case ND_LT:
   case ND_LE:
   case ND_NUM:
+  case ND_NOT:
     node->ty = long_type;
     return;
   case ND_PTR_ADD: