diff --git a/src/string_utils.h b/src/string_utils.h
index ac37ef7a..7c1b7bcf 100644
--- a/src/string_utils.h
+++ b/src/string_utils.h
@@ -19,10 +19,15 @@ Utilities for manipulating strings in C.
 
 #define MAX_UTF8_CHAR_SIZE 4
 
-#define INT8_MAX_STRING_SIZE 5
-#define INT16_MAX_STRING_SIZE 7
-#define INT32_MAX_STRING_SIZE 11
-#define INT64_MAX_STRING_SIZE 21
+#define INT8_MAX_STRING_LEN 5
+#define INT8_MAX_STRING_SIZE INT8_MAX_STRING_LEN + 1
+#define INT16_MAX_STRING_LEN 7
+#define INT16_MAX_STRING_SIZE INT16_MAX_STRING_LEN + 1
+#define INT32_MAX_STRING_LEN 11
+#define INT32_MAX_STRING_SIZE INT32_MAX_STRING_LEN + 1
+#define INT64_MAX_STRING_LEN 21
+#define INT64_MAX_STRING_SIZE INT64_MAX_STRING_LEN + 1
+
 
 #define UTF8PROC_OPTIONS_BASE UTF8PROC_NULLTERM | UTF8PROC_STABLE