diff --git a/bin/tests/system/kasp.sh b/bin/tests/system/kasp.sh
index f0c83b19ab..d49baa3047 100644
--- a/bin/tests/system/kasp.sh
+++ b/bin/tests/system/kasp.sh
@@ -725,6 +725,7 @@ check_numkeys() {
 
 _check_keys() {
 	ret=0
+	_ret=0
 
 	# Clear key ids.
 	key_set KEY1 ID "no"
@@ -767,10 +768,10 @@ _check_keys() {
 
 		# If ret is still non-zero, none of the files matched.
 		echo_i "failed"
-		return 1
+		_ret=1
 	done
 
-	return 0
+	return $_ret
 }
 
 # Check keys for a configured zone. This verifies:
diff --git a/bin/tests/system/kasp/ns3/named-fips.conf.in b/bin/tests/system/kasp/ns3/named-fips.conf.in
index 6199b0496b..b14b142eff 100644
--- a/bin/tests/system/kasp/ns3/named-fips.conf.in
+++ b/bin/tests/system/kasp/ns3/named-fips.conf.in
@@ -240,6 +240,17 @@ zone "max-zone-ttl.kasp" {
 	dnssec-policy "ttl";
 };
 
+/*
+ * Zone for testing GL #2375: Three is a crowd.
+ */
+zone "three-is-a-crowd.kasp" {
+	type primary;
+	file "three-is-a-crowd.kasp.db";
+	inline-signing yes;
+	/* Use same policy as KSK rollover test zones. */
+	dnssec-policy "ksk-doubleksk";
+};
+
 /*
  * Zones in different signing states.
  */
diff --git a/bin/tests/system/kasp/ns3/setup.sh b/bin/tests/system/kasp/ns3/setup.sh
index 21e6356267..8682f54dcb 100644
--- a/bin/tests/system/kasp/ns3/setup.sh
+++ b/bin/tests/system/kasp/ns3/setup.sh
@@ -1427,3 +1427,44 @@ private_type_record $zone $DEFAULT_ALGORITHM_NUMBER "$CSK1" >> "$infile"
 private_type_record $zone $DEFAULT_ALGORITHM_NUMBER "$CSK2" >> "$infile"
 cp $infile $zonefile
 $SIGNER -S -z -x -s now-1h -e now+30d -o $zone -O raw -f "${zonefile}.signed" $infile > signer.out.$zone.1 2>&1
+
+# Test #2375, the "three is a crowd" bug, where a new key is introduced but the
+# previous rollover has not finished yet. In other words, we have a key KEY2
+# that is the successor of key KEY1, and we introduce a new key KEY3 that is
+# the successor of key KEY2:
+#
+#     KEY1 < KEY2 < KEY3.
+#
+# The expected behavior is that all three keys remain in the zone, and not
+# the bug behavior where KEY2 is removed and immediately replaced with KEY3.
+#
+# Set up a zone that has a KSK (KEY1) and have the successor key (KEY2)
+# published as well.
+setup three-is-a-crowd.kasp
+# These times are the same as step3.ksk-doubleksk.autosign.
+TactN="now-60d"
+TretN="now"
+TremN="now+50h"
+TpubN1="now-27h"
+TsbmN1="now"
+TactN1="${TretN}"
+TretN1="now+60d"
+TremN1="now+1490h"
+ksktimes="-P ${TactN}  -A ${TactN}  -P sync ${TactN}  -I ${TretN}  -D ${TremN}"
+newtimes="-P ${TpubN1} -A ${TactN1} -P sync ${TsbmN1} -I ${TretN1} -D ${TremN1}"
+zsktimes="-P ${TactN}  -A ${TactN}"
+KSK1=$($KEYGEN -a $DEFAULT_ALGORITHM -L 7200 -f KSK $ksktimes $zone 2> keygen.out.$zone.1)
+KSK2=$($KEYGEN -a $DEFAULT_ALGORITHM -L 7200 -f KSK $newtimes $zone 2> keygen.out.$zone.2)
+ZSK=$($KEYGEN  -a $DEFAULT_ALGORITHM -L 7200        $zsktimes $zone 2> keygen.out.$zone.3)
+$SETTIME -s -g $H -k $O $TactN   -r $O $TactN  -d $O $TactN  "$KSK1" > settime.out.$zone.1 2>&1
+$SETTIME -s -g $O -k $R $TpubN1  -r $R $TpubN1 -d $H $TpubN1 "$KSK2" > settime.out.$zone.2 2>&1
+$SETTIME -s -g $O -k $O $TactN   -z $O $TactN                "$ZSK"  > settime.out.$zone.3 2>&1
+# Set key rollover relationship.
+key_successor $KSK1 $KSK2
+# Sign zone.
+cat template.db.in "${KSK1}.key" "${KSK2}.key" "${ZSK}.key" > "$infile"
+private_type_record $zone $DEFAULT_ALGORITHM_NUMBER "$KSK1" >> "$infile"
+private_type_record $zone $DEFAULT_ALGORITHM_NUMBER "$KSK2" >> "$infile"
+private_type_record $zone $DEFAULT_ALGORITHM_NUMBER "$ZSK" >> "$infile"
+cp $infile $zonefile
+$SIGNER -S -x -s now-1h -e now+2w -o $zone -O raw -f "${zonefile}.signed" $infile > signer.out.$zone.1 2>&1
diff --git a/bin/tests/system/kasp/tests.sh b/bin/tests/system/kasp/tests.sh
index fbb8bdc215..4d3bda7737 100644
--- a/bin/tests/system/kasp/tests.sh
+++ b/bin/tests/system/kasp/tests.sh
@@ -3545,10 +3545,81 @@ dnssec_verify
 #
 # Test #2375: Scheduled rollovers are happening faster than they can finish
 #
-set_zone "step1.three-is-a-crowd.kasp"
-set_policy "default" "1" "3600"
+set_zone "three-is-a-crowd.kasp"
+set_policy "ksk-doubleksk" "3" "7200"
 set_server "ns3" "10.53.0.3"
-# TODO (GL #2471).
+CDNSKEY="no"
+# These are the same time values as calculated for ksk-doubleksk.
+Lksk=5184000
+Lzsk=31536000
+IretKSK=180000
+IretZSK=867600
+# KSK (KEY1) is outgoing.
+key_clear        "KEY1"
+set_keyrole      "KEY1" "ksk"
+set_keylifetime  "KEY1" "${Lksk}"
+set_keyalgorithm "KEY1" "$DEFAULT_ALGORITHM_NUMBER" "$DEFAULT_ALGORITHM" "$DEFAULT_BITS"
+set_keysigning   "KEY1" "yes"
+set_zonesigning  "KEY1" "yes"
+set_keystate     "KEY1" "GOAL"         "hidden"
+set_keystate     "KEY1" "STATE_DNSKEY" "omnipresent"
+set_keystate     "KEY1" "STATE_KRRSIG" "omnipresent"
+set_keystate     "KEY1" "STATE_DS"     "unretentive"
+# KSK (KEY2) is incoming.
+key_clear        "KEY2"
+set_keyrole      "KEY2" "ksk"
+set_keylifetime  "KEY2" "${Lksk}"
+set_keyalgorithm "KEY2" "$DEFAULT_ALGORITHM_NUMBER" "$DEFAULT_ALGORITHM" "$DEFAULT_BITS"
+set_keysigning   "KEY2" "yes"
+set_zonesigning  "KEY2" "no"
+set_keystate     "KEY2" "GOAL"         "omnipresent"
+set_keystate     "KEY2" "STATE_DNSKEY" "omnipresent"
+set_keystate     "KEY2" "STATE_KRRSIG" "omnipresent"
+set_keystate     "KEY2" "STATE_DS"     "rumoured"
+# We will introduce the third KSK shortly.
+key_clear        "KEY3"
+# ZSK (KEY4).
+key_clear        "KEY4"
+set_keyrole      "KEY4" "zsk"
+set_keylifetime  "KEY4" "${Lzsk}"
+set_keyalgorithm "KEY4" "$DEFAULT_ALGORITHM_NUMBER" "$DEFAULT_ALGORITHM" "$DEFAULT_BITS"
+set_keysigning   "KEY4" "no"
+set_zonesigning  "KEY4" "yes"
+set_keystate     "KEY4" "GOAL"         "omnipresent"
+set_keystate     "KEY4" "STATE_DNSKEY" "omnipresent"
+set_keystate     "KEY4" "STATE_ZRRSIG" "omnipresent"
+# Run preliminary tests.
+check_keys
+check_dnssecstatus "$SERVER" "$POLICY" "$ZONE"
+check_apex
+check_subdomain
+dnssec_verify
+# Roll over KEY2.
+# Set expected key lifetime, which is DNSKEY TTL plus the zone propagation delay,
+# plus the publish-safety: 7200s + 1h + 1d = 97200 seconds.
+set_keylifetime  "KEY2" "97200"
+created=$(key_get KEY2 CREATED)
+rndc_rollover "$SERVER" "$DIR" $(key_get KEY2 ID) "${created}" "$ZONE"
+# Update expected number of keys and key states.
+set_keystate "KEY2" "GOAL" "hidden"
+set_policy "ksk-doubleksk" "4" "7200"
+CDNSKEY="no"
+# New KSK (KEY3) is introduced.
+set_keyrole      "KEY3" "ksk"
+set_keylifetime  "KEY3" "${Lksk}"
+set_keyalgorithm "KEY3" "$DEFAULT_ALGORITHM_NUMBER" "$DEFAULT_ALGORITHM" "$DEFAULT_BITS"
+set_keysigning   "KEY3" "yes"
+set_zonesigning  "KEY3" "no"
+set_keystate     "KEY3" "GOAL"         "omnipresent"
+set_keystate     "KEY3" "STATE_DNSKEY" "rumoured"
+set_keystate     "KEY3" "STATE_KRRSIG" "rumoured"
+set_keystate     "KEY3" "STATE_DS"     "hidden"
+# Run tests again. We now expect four keys (3x KSK, 1x ZSK).
+check_keys
+check_dnssecstatus "$SERVER" "$POLICY" "$ZONE"
+check_apex
+check_subdomain
+dnssec_verify
 
 # Test dynamic zones that switch to inline-signing.
 set_zone "dynamic2inline.kasp"