diff --git a/CHANGES b/CHANGES
index 9545d7e4a3..7818ade44e 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,7 @@
+5815.	[bug]		If an oversized key name of a specific length was used
+			in the text form of an HTTP or SVBC record, an INSIST
+			could be triggered when parsing it. [GL #3175]
+
 5814.	[bug]		The RecursClients statistics counter could underflow
 			in certain resolution scenarios. [GL #3147]
 
diff --git a/fuzz/dns_rdata_fromtext.in/svbc-max-token b/fuzz/dns_rdata_fromtext.in/svbc-max-token
new file mode 100644
index 0000000000..6d1a265d9f
--- /dev/null
+++ b/fuzz/dns_rdata_fromtext.in/svbc-max-token
@@ -0,0 +1 @@
+1 65 8 . aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa=
diff --git a/lib/isc/lex.c b/lib/isc/lex.c
index 9546553800..aa9b549f79 100644
--- a/lib/isc/lex.c
+++ b/lib/isc/lex.c
@@ -670,6 +670,13 @@ isc_lex_gettoken(isc_lex_t *lex, unsigned int options, isc_token_t *tokenp) {
 		case lexstate_string:
 			if (!escaped && c == '=' &&
 			    (options & ISC_LEXOPT_VPAIR) != 0) {
+				if (remaining == 0U) {
+					result = grow_data(lex, &remaining,
+							   &curr, &prev);
+					if (result != ISC_R_SUCCESS) {
+						goto done;
+					}
+				}
 				INSIST(remaining > 0U);
 				*curr++ = c;
 				*curr = '\0';
@@ -682,7 +689,6 @@ isc_lex_gettoken(isc_lex_t *lex, unsigned int options, isc_token_t *tokenp) {
 			if (state == lexstate_vpairstart) {
 				if (c == '"' &&
 				    (options & ISC_LEXOPT_QVPAIR) != 0) {
-					INSIST(remaining > 0U);
 					no_comments = true;
 					state = lexstate_qvpair;
 					break;