diff --git a/util/cutils.c b/util/cutils.c
index 2380165230..36ce712271 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -542,7 +542,7 @@ int qemu_strtoul(const char *nptr, const char **endptr, int base,
  * Convert string @nptr to an int64_t.
  *
  * Works like qemu_strtol(), except it stores INT64_MAX on overflow,
- * and INT_MIN on underflow.
+ * and INT64_MIN on underflow.
  */
 int qemu_strtoi64(const char *nptr, const char **endptr, int base,
                  int64_t *result)
@@ -557,8 +557,9 @@ int qemu_strtoi64(const char *nptr, const char **endptr, int base,
         return -EINVAL;
     }
 
+    /* This assumes int64_t is long long TODO relax */
+    QEMU_BUILD_BUG_ON(sizeof(int64_t) != sizeof(long long));
     errno = 0;
-    /* FIXME This assumes int64_t is long long */
     *result = strtoll(nptr, &ep, base);
     return check_strtox_error(nptr, ep, endptr, errno);
 }
@@ -581,8 +582,9 @@ int qemu_strtou64(const char *nptr, const char **endptr, int base,
         return -EINVAL;
     }
 
+    /* This assumes uint64_t is unsigned long long TODO relax */
+    QEMU_BUILD_BUG_ON(sizeof(uint64_t) != sizeof(unsigned long long));
     errno = 0;
-    /* FIXME This assumes uint64_t is unsigned long long */
     *result = strtoull(nptr, &ep, base);
     /* Windows returns 1 for negative out-of-range values.  */
     if (errno == ERANGE) {