diff --git a/bin/plugins/synthrecord.c b/bin/plugins/synthrecord.c
index 4f7bff17b4..f586d3f9e0 100644
--- a/bin/plugins/synthrecord.c
+++ b/bin/plugins/synthrecord.c
@@ -67,7 +67,7 @@ synthrecord_reverseanswer(synthrecord_t *inst, isc_netaddr_t *na,
 	REQUIRE(na->family == AF_INET || na->family == AF_INET6);
 
 	isc_buffer_init(&b, bdata, sizeof(bdata));
-	isc_buffer_copyregion(&b, &inst->prefix);
+	RETERR(isc_buffer_copyregion(&b, &inst->prefix));
 
 	isc_buffer_init(&addrb, addrbdata, sizeof(addrbdata));
 	RETERR(isc_netaddr_totext(na, &addrb));
@@ -86,6 +86,9 @@ synthrecord_reverseanswer(synthrecord_t *inst, isc_netaddr_t *na,
 		 */
 		isc_buffer_peekuint8(&addrb, &c);
 		if (c == ':') {
+			if (isc_buffer_availablelength(&b) == 0) {
+				return ISC_R_NOSPACE;
+			}
 			isc_buffer_putuint8(&b, '0');
 		}
 
@@ -96,12 +99,15 @@ synthrecord_reverseanswer(synthrecord_t *inst, isc_netaddr_t *na,
 		isc_buffer_forward(&addrb, isc_buffer_usedlength(&addrb) - 1);
 		isc_buffer_peekuint8(&addrb, &c);
 		if (c == ':') {
+			if (isc_buffer_availablelength(&b) == 0) {
+				return ISC_R_NOSPACE;
+			}
 			isc_buffer_putuint8(&addrb, '0');
 		}
 	}
 
 	isc_buffer_usedregion(&addrb, &addrr);
-	isc_buffer_copyregion(&b, &addrr);
+	RETERR(isc_buffer_copyregion(&b, &addrr));
 
 	/*
 	 * Do not attempt to replace anything in the prefix
@@ -214,6 +220,13 @@ synthrecord_parseforward(synthrecord_t *inst, const dns_name_t *name,
 
 	isc_buffer_init(&b, bdata, sizeof(bdata));
 	dns_name_totext(&label, DNS_NAME_OMITFINALDOT, &b);
+
+	/*
+	 * Buffer is `DNS_NAME_FORMATSIZE` which is the maximum length of
+	 * `dns_name_totext()` can put in there, plus one byte which we're
+	 * setting here. So we know there is at least one remaining byte in the
+	 * buffer.
+	 */
 	isc_buffer_putuint8(&b, 0);
 	if (strncmp((const char *)inst->prefix.base, isc_buffer_base(&b),
 		    inst->prefix.length) != 0)
diff --git a/bin/tests/system/synthrecord/ns1/named.conf.j2 b/bin/tests/system/synthrecord/ns1/named.conf.j2
index f2421febb1..0193196b1f 100644
--- a/bin/tests/system/synthrecord/ns1/named.conf.j2
+++ b/bin/tests/system/synthrecord/ns1/named.conf.j2
@@ -1,4 +1,5 @@
 {% set inview = inview | default(False) %}
+{% set toolongprefix = toolongprefix | default(False) %}
 
 options {
 	query-source address 10.53.0.1;
@@ -56,7 +57,11 @@ zone "0.53.10.in-addr.arpa." {
 	type primary;
 	file "0.53.10.in-addr.arpa.db";
 	plugin query "@TOP_BUILDDIR@/synthrecord" {
+{% if toolongprefix %}
+		prefix "waytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefixwaytoolongprefix";
+{% else %}
 		prefix "dynamic-";
+{% endif %}
 		allow-synth {
 			10.53.0.0/24;
 		};
diff --git a/bin/tests/system/synthrecord/tests_synthrecord.py b/bin/tests/system/synthrecord/tests_synthrecord.py
index 3579b7a33d..dc66d9fe5f 100644
--- a/bin/tests/system/synthrecord/tests_synthrecord.py
+++ b/bin/tests/system/synthrecord/tests_synthrecord.py
@@ -508,3 +508,18 @@ def test_synthrecord_inview(ns1, templates):
         cmd = ns1.rndc("reconfig", raise_on_exception=False)
         assert cmd.rc != 0
         watcher.wait_for_line("'synthrecord' must be configured as a zone plugin")
+
+
+def test_synthrecord_toolongprefix(ns1, templates):
+    templates.render("ns1/named.conf", {"toolongprefix": True})
+    with ns1.watch_log_from_here() as watcher:
+        ns1.rndc("reconfig")
+        watcher.wait_for_line("running")
+    ip = IPv4Address("10.53.0.8")
+    with ns1.watch_log_from_here() as watcher:
+        query = dns.message.make_query(ip.reverse_pointer, "PTR")
+        res = isctest.query.udp(query, SERVER)
+        assert res.rcode() == dns.rcode.NXDOMAIN
+        watcher.wait_for_line(
+            "synthrecord cannot create reverse answer name: ran out of space"
+        )