diff --git a/ChangeLog b/ChangeLog
index 34a47bb..130afaa 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -286,6 +286,8 @@ a factor of the size of the compiling workspace (it currently is).
 
 83. Lock out configuring for EBCDIC with non-8-bit libraries.
 
+84. Test for error code <= 0 in regerror().
+
 
 Version 10.20 30-June-2015
 --------------------------
diff --git a/src/pcre2posix.c b/src/pcre2posix.c
index 134a0c1..2792c17 100644
--- a/src/pcre2posix.c
+++ b/src/pcre2posix.c
@@ -147,7 +147,7 @@ regerror(int errcode, const regex_t *preg, char *errbuf, size_t errbuf_size)
 int used;
 const char *message;
 
-message = (errcode >= (int)(sizeof(pstring)/sizeof(char *)))?
+message = (errcode <= 0 || errcode >= (int)(sizeof(pstring)/sizeof(char *)))?
   "unknown error code" : pstring[errcode];
 
 if (preg != NULL && (int)preg->re_erroffset != -1)