diff --git a/preprocess.c b/preprocess.c
index 82a0ef383333f46c6c964944f47c116869bae9f6..bfaa9b55be09e7ad9544e59502f0b8d0494d556c 100644
--- a/preprocess.c
+++ b/preprocess.c
@@ -20,6 +20,8 @@ struct CondIncl {
 static Macro *macros;
 static CondIncl *cond_incl;
 
+static Token *preprocess2(Token *tok);
+
 static char *format(char *fmt, ...) {
   va_list ap;
   va_start(ap, fmt);
@@ -31,6 +33,7 @@ static char *format(char *fmt, ...) {
   fclose(out);
   return buf;
 }
+
 static bool is_hash(Token *tok) {
   return tok->at_bol && equal(tok, "#");
 }
@@ -124,6 +127,7 @@ static Token *copy_line(Token **rest, Token *tok) {
 static long eval_const_expr(Token **rest, Token *tok) {
   Token *start = tok;
   Token *expr = copy_line(rest, tok->next);
+  expr = preprocess2(expr);
 
   if (expr->kind == TK_EOF)
     error_tok(start, "no expression");
diff --git a/test/macro.c b/test/macro.c
index 6481464a2438eace6bc5138f4b2598a20231d2bf..61447f6efca67dbf4809402f029926672fa74b49 100644
--- a/test/macro.c
+++ b/test/macro.c
@@ -128,6 +128,22 @@ int main() {
 
   if (0);
 
+#define M 5
+#if M
+  m = 5;
+#else
+  m = 6;
+#endif
+  assert(5, m, "m");
+
+#define M 5
+#if M-5
+  m = 6;
+#elif M
+  m = 5;
+#endif
+  assert(5, m, "m");
+
   printf("OK\n");
   return 0;
 }