diff --git a/CHANGES b/CHANGES
index b8ea0b1602..f96de23205 100644
--- a/CHANGES
+++ b/CHANGES
@@ -1,3 +1,7 @@
+5711.	[bug]		"map" files exceeding 2GB in size could fail to
+			load due to a size comparison that incorrectly
+			treated the file size as a signed integer. [GL #2878]
+
 5710.	[placeholder]
 
 5709.	[func]		Zone types are now reported in the statistics channel
@@ -34,7 +38,7 @@
 5701.	[bug]		named-checkconf failed to detect syntactically invalid
 			key and tls names. [GL #2461]
 
-5700.	[bug]		Journals where not being removed when a catalog zone
+5700.	[bug]		Journals were not being removed when a catalog zone
 			was removed. [GL #2842]
 
 5699.	[func]		Grow and shrink dnssec-sign statistics on key rollover
diff --git a/bin/tests/system/masterformat/clean.sh b/bin/tests/system/masterformat/clean.sh
index 80289e9267..82502fc430 100755
--- a/bin/tests/system/masterformat/clean.sh
+++ b/bin/tests/system/masterformat/clean.sh
@@ -26,7 +26,7 @@ rm -f ./ns2/formerly-text.db
 rm -f ./ns2/db-*
 rm -f ./ns2/large.bk
 rm -f ./ns3/example.db.map ./ns3/dynamic.db.map
-rm -f ./baseline.txt ./text.1 ./text.2 ./raw.1 ./raw.2 ./map.1 ./map.2 ./map.5 ./text.5 ./badmap
+rm -f ./baseline.txt ./text.* ./raw.* ./map.* ./badmap
 rm -f ./ns1/Ksigned.* ./ns1/dsset-signed. ./ns1/signed.db.signed
 rm -f ./rndc.out
 rm -f ./ns*/named.lock
diff --git a/bin/tests/system/masterformat/tests.sh b/bin/tests/system/masterformat/tests.sh
index d17f4983b5..6a0453e185 100755
--- a/bin/tests/system/masterformat/tests.sh
+++ b/bin/tests/system/masterformat/tests.sh
@@ -330,5 +330,22 @@ n=$((n+1))
 [ $ret -eq 0 ] || echo_i "failed"
 status=$((status+ret))
 
+# The following test is disabled by default because it is very slow.
+if [ -n "${TEST_LARGE_MAP}" ]; then
+    echo_i "checking map file size > 2GB can be loaded ($n)"
+    ret=0
+    $PERL ../../startperf/mkzonefile.pl test 9000000 > text.$n
+    # convert to map
+    $CHECKZONE -D -f text -F map -o map.$n test text.$n > /dev/null || ret=1
+    # check map file size is over 2GB to ensure the test is valid
+    size=$(ls -l map.$n | awk '{print $5}')
+    [ "$size" -gt 2147483648 ] || ret=1
+    # convert back to text
+    $CHECKZONE -f map test map.$n > /dev/null || ret=1
+    n=$((n+1))
+    [ $ret -eq 0 ] || echo_i "failed"
+    status=$((status+ret))
+fi
+
 echo_i "exit status: $status"
 [ $status -eq 0 ] || exit 1
diff --git a/bin/tests/system/run.sh.in b/bin/tests/system/run.sh.in
index b4d14cd8cf..bd4c38e843 100644
--- a/bin/tests/system/run.sh.in
+++ b/bin/tests/system/run.sh.in
@@ -72,7 +72,7 @@ if ! $do_run; then
     if [ "$baseport" -eq 0 ]; then
         log_flags="$log_flags -p 5300"
     fi
-    env - CYGWIN="$CYGWIN" SYSTEMTEST_FORCE_COLOR="$SYSTEMTEST_FORCE_COLOR" SYSTEMTEST_NO_CLEAN="$SYSTEMTEST_NO_CLEAN" SLOT="$SLOT" SOFTHSM2_CONF="$SOFTHSM2_CONF" PATH="$PATH" ${LD_LIBRARY_PATH:+"LD_LIBRARY_PATH=${LD_LIBRARY_PATH}"} TESTS="$*" TEST_SUITE_LOG=run.log LOG_DRIVER_FLAGS="--verbose yes --color-tests yes" LOG_FLAGS="$log_flags" make -e check
+    env - CYGWIN="$CYGWIN" SYSTEMTEST_FORCE_COLOR="$SYSTEMTEST_FORCE_COLOR" SYSTEMTEST_NO_CLEAN="$SYSTEMTEST_NO_CLEAN" SLOT="$SLOT" SOFTHSM2_CONF="$SOFTHSM2_CONF" PATH="$PATH" ${LD_LIBRARY_PATH:+"LD_LIBRARY_PATH=${LD_LIBRARY_PATH}"} TESTS="$*" TEST_SUITE_LOG=run.log LOG_DRIVER_FLAGS="--verbose yes --color-tests yes" LOG_FLAGS="$log_flags" TEST_LARGE_MAP="${TEST_LARGE_MAP}" make -e check
     exit $?
 fi
 
diff --git a/lib/dns/rbt.c b/lib/dns/rbt.c
index 4cfc1769af..f845725f47 100644
--- a/lib/dns/rbt.c
+++ b/lib/dns/rbt.c
@@ -775,17 +775,18 @@ treefix(dns_rbt_t *rbt, void *base, size_t filesize, dns_rbtnode_t *n,
 	uint64_t *crc) {
 	isc_result_t result = ISC_R_SUCCESS;
 	dns_fixedname_t fixed;
-	dns_name_t nodename, *fullname;
-	unsigned char *node_data;
+	dns_name_t nodename, *fullname = NULL;
+	unsigned char *node_data = NULL;
 	dns_rbtnode_t header;
-	size_t datasize, nodemax = filesize - sizeof(dns_rbtnode_t);
+	size_t nodemax = filesize - sizeof(dns_rbtnode_t);
+	size_t datasize;
 
 	if (n == NULL) {
 		return (ISC_R_SUCCESS);
 	}
 
 	CONFIRM((void *)n >= base);
-	CONFIRM((char *)n - (char *)base <= (int)nodemax);
+	CONFIRM((size_t)((char *)n - (char *)base) <= nodemax);
 	CONFIRM(DNS_RBTNODE_VALID(n));
 
 	dns_name_init(&nodename, NULL);
diff --git a/lib/dns/rbtdb.c b/lib/dns/rbtdb.c
index 3b5035ea34..a5068d0f3a 100644
--- a/lib/dns/rbtdb.c
+++ b/lib/dns/rbtdb.c
@@ -7579,7 +7579,7 @@ rbt_datafixer(dns_rbtnode_t *rbtnode, void *base, size_t filesize, void *arg,
  * Load the RBT database from the image in 'f'
  */
 static isc_result_t
-deserialize32(void *arg, FILE *f, off_t offset) {
+deserialize(void *arg, FILE *f, off_t offset) {
 	isc_result_t result;
 	rbtdb_load_t *loadctx = arg;
 	dns_rbtdb_t *rbtdb = loadctx->rbtdb;
@@ -7724,7 +7724,7 @@ beginload(dns_db_t *db, dns_rdatacallbacks_t *callbacks) {
 
 	callbacks->add = loading_addrdataset;
 	callbacks->add_private = loadctx;
-	callbacks->deserialize = deserialize32;
+	callbacks->deserialize = deserialize;
 	callbacks->deserialize_private = loadctx;
 
 	return (ISC_R_SUCCESS);