diff --git a/src/configuration.c b/src/configuration.c
index e8142a9..4874765 100644
--- a/src/configuration.c
+++ b/src/configuration.c
@@ -57,6 +57,7 @@ static char *strip_quotes(char *val)
 static int text2port(const char *value, int *port)
 {
   char *end;
+  errno = 0;
   long n = strtol(value, &end, 10);
 
   if (value == end || errno == ERANGE || *trim(end) != '\0' ||