diff --git a/include/fast_float/ascii_number.h b/include/fast_float/ascii_number.h
index 5c82c6c..f37241c 100644
--- a/include/fast_float/ascii_number.h
+++ b/include/fast_float/ascii_number.h
@@ -468,7 +468,7 @@ from_chars_result_t<UC> parse_int_string(UC const* p, UC const* pend, T& value,
   uint64_t i = 0;
   while (p != pend) {
     uint8_t digit = ch_to_digit(*p);
-    if (digit > base) {
+    if (digit >= base) {
       break;
     }
     i = uint64_t(base) * i + digit; // might overflow, check this later
diff --git a/include/fast_float/parse_number.h b/include/fast_float/parse_number.h
index 4c75f5d..1fd587b 100644
--- a/include/fast_float/parse_number.h
+++ b/include/fast_float/parse_number.h
@@ -242,7 +242,7 @@ from_chars_result_t<UC> from_chars(UC const* first, UC const* last, T& value, in
     first++;
   }
 #endif
-  if (first == last) {
+  if (first == last || base < 2 || base > 36) {
     answer.ec = std::errc::invalid_argument;
     answer.ptr = first;
     return answer;