diff --git a/tcctest.c b/tcctest.c
index 012a51b9..bc6818bf 100644
--- a/tcctest.c
+++ b/tcctest.c
@@ -1420,6 +1420,8 @@ void prefix ## cmp(type a, type b)\
     printf(fmt "\n", ++a);\
     printf(fmt "\n", a++);\
     printf(fmt "\n", a);\
+    b = 0;\
+    printf("%d %d\n", !a, !b);\
 }\
 void prefix ## fcast(type a)\
 {\
@@ -1583,6 +1585,8 @@ void lloptest(long long a, long long b)
     printf("arith2: %Ld %Ld\n", a++, b++);
     printf("arith2: %Ld %Ld\n", --a, --b);
     printf("arith2: %Ld %Ld\n", a, b);
+    b = ub = 0;
+    printf("not: %d %d %d %d\n", !a, !ua, !b, !ub);
 }
 
 void llshift(long long a, int b)
diff --git a/x86_64-gen.c b/x86_64-gen.c
index 1d0d8db6..1227f41f 100644
--- a/x86_64-gen.c
+++ b/x86_64-gen.c
@@ -888,7 +888,6 @@ int gtst(int inv, int t)
             gsym(vtop->c.i);
         }
     } else {
-        /* XXX: not tested */
         if (is_float(vtop->type.t) ||
             (vtop->type.t & VT_BTYPE) == VT_LLONG) {
             vpushi(0);