1 files changed, 1 insertions, 1 deletions
diff --git a/hex.c b/hex.c
index ac1705f3..635bd53a 100644
--- a/hex.c
+++ b/hex.c
@@ -17,7 +17,7 @@ const char /*@ observer @*/ *gpsd_packetdump(char *scbuf, size_t scbuflen,
 
     assert(binbuf != NULL);
     for (cp = binbuf; cp < binbuf + binbuflen; cp++)
-	if (!isprint(*cp) && !isspace(*cp))
+	if (!isprint((unsigned char) *cp) && !isspace((unsigned char) *cp))
 	    printable = false;
     if (printable)
 	return binbuf;