diff --git a/parse.c b/parse.c
index ddec052..1aae37a 100644
--- a/parse.c
+++ b/parse.c
@@ -2841,8 +2841,16 @@ static Node *primary(Token **rest, Token *tok) {
   if (equal(tok, "sizeof") && equal(tok->next, "(") && is_typename(tok->next->next)) {
     Type *ty = typename(&tok, tok->next->next);
     *rest = skip(tok, ")");
-    if (ty->kind == TY_VLA)
-      return new_var_node(ty->vla_size, tok);
+
+    if (ty->kind == TY_VLA) {
+      if (ty->vla_size)
+        return new_var_node(ty->vla_size, tok);
+
+      Node *lhs = compute_vla_size(ty, tok);
+      Node *rhs = new_var_node(ty->vla_size, tok);
+      return new_binary(ND_COMMA, lhs, rhs, tok);
+    }
+
     return new_ulong(ty->size, start);
   }
 
diff --git a/test/vla.c b/test/vla.c
index 60c6dfb..b0efd4a 100644
--- a/test/vla.c
+++ b/test/vla.c
@@ -19,6 +19,8 @@ int main() {
   ASSERT(5, ({ int n=10; int x[n+1][n+6]; int *p=x; for (int i = 0; i<sizeof(x)/4; i++) p[i]=i; x[0][5]; }));
   ASSERT(5*16+2, ({ int n=10; int x[n+1][n+6]; int *p=x; for (int i = 0; i<sizeof(x)/4; i++) p[i]=i; x[5][2]; }));
 
+  ASSERT(10, ({ int n=5; sizeof(char[2][n]); }));
+
   printf("OK\n");
   return 0;
 }