diff --git a/CHANGES b/CHANGES
index 8ff0bf79e2..fbcc8321d2 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,9 @@
+4090.	[bug]		Fix a crash while parsing malformed CAA RRs in
+			presentation format, i.e., from text such as
+			from master files. Thanks to John Van de
+			Meulebrouck Brendgard for discovering and
+			reporting this problem. [RT #39003]
+
 4089.	[bug]		Send notifies immediately for slave zones during
 			startup. [RT #38843]
 
diff --git a/bin/tests/system/checkzone/zones/bad-caa-rr.db b/bin/tests/system/checkzone/zones/bad-caa-rr.db
new file mode 100644
index 0000000000..9a763a86a6
Binary files /dev/null and b/bin/tests/system/checkzone/zones/bad-caa-rr.db differ
diff --git a/lib/dns/rdata/generic/caa_257.c b/lib/dns/rdata/generic/caa_257.c
index 3ca1723c55..75af983e34 100644
--- a/lib/dns/rdata/generic/caa_257.c
+++ b/lib/dns/rdata/generic/caa_257.c
@@ -68,7 +68,7 @@ fromtext_caa(ARGS_FROMTEXT) {
 				      ISC_FALSE));
 	tr = token.value.as_textregion;
 	for (i = 0; i < tr.length; i++)
-		if (!alphanumeric[(unsigned int) tr.base[i]])
+		if (!alphanumeric[(unsigned char) tr.base[i]])
 			RETTOK(DNS_R_SYNTAX);
 	RETERR(uint8_tobuffer(tr.length, target));
 	RETERR(mem_tobuffer(target, tr.base, tr.length));