diff --git a/Makefile b/Makefile
index 59a200f..b472c8f 100644
--- a/Makefile
+++ b/Makefile
@@ -55,8 +55,8 @@ refdata/RDAMediaType.nt:
 %-preprocessed.alephseq: %-in.alephseq
 	uniq $< | scripts/filter-duplicates.py | $(UCONV) -x Any-NFC -i | scripts/filter-fennica-repl.py >$@
 
-%.mrcx: %-preprocessed.alephseq refdata/iso639-2-fi.csv
-	$(CATMANDU) convert MARC --type ALEPHSEQ to MARC --type XML --fix scripts/filter-marc.fix --fix scripts/strip-personal-info.fix --fix scripts/preprocess-marc.fix <$< >$@
+%.mrcx: %-preprocessed.alephseq refdata/iso639-2-fi.csv refdata/subst-260c.csv
+	$(CATMANDU) convert MARC --type ALEPHSEQ to MARC --type XML --fix scripts/filter-marc.fix --fix scripts/strip-personal-info.fix --fix scripts/preprocess-marc.fix --fix scripts/substitute-marc.fix <$< >$@
 
 %-bf2.rdf: %.mrcx
 	$(XSLTPROC) --stringparam baseuri $(URIBASEFENNICA) $(MARC2BIBFRAME2)/xsl/marc2bibframe2.xsl $^ >$@
diff --git a/scripts/extract-subst-260c.py b/scripts/extract-subst-260c.py
new file mode 100755
index 0000000..9d4486e
--- /dev/null
+++ b/scripts/extract-subst-260c.py
@@ -0,0 +1,44 @@
+#!/usr/bin/env python3
+
+import sys
+import csv
+
+reader = csv.reader(sys.stdin, dialect='excel-tab')
+writer = csv.writer(sys.stdout, quoting=csv.QUOTE_ALL)
+
+for lineno, row in enumerate(reader):
+    if lineno == 0:
+        continue  # skip header
+
+    recid = row[0]
+    orig260c = row[1]
+    new260c_from = row[4]
+    new260c_till = row[5]
+
+    key = recid + "/" + orig260c
+    val = new260c_from
+    
+    if new260c_till:
+        val += "-" + new260c_till
+
+    # skip trivial cases (already handled by conversion)    
+    if orig260c == val:
+        continue
+
+    if orig260c == val + ".":
+        continue
+
+    if orig260c == val + "-":
+        continue
+
+    if orig260c == val + "-.":
+        continue
+
+    if orig260c == "[" + val + "]":
+        continue
+
+    if orig260c == "[" + val + "].":
+        continue
+
+    
+    writer.writerow([key, val])
diff --git a/scripts/substitute-marc.fix b/scripts/substitute-marc.fix
new file mode 100644
index 0000000..dec9239
--- /dev/null
+++ b/scripts/substitute-marc.fix
@@ -0,0 +1,11 @@
+# Apply cleanup substitutions from CSV files to MARC records
+
+marc_map('001',recid)
+marc_map('260c',orig260c)
+if exists(orig260c)
+	paste(substval,recid,orig260c,join_char:"/")
+	lookup(substval,'refdata/subst-260c.csv',delete:1)
+	if exists(substval)
+		marc_set('260c',$.substval)
+	end
+end
diff --git a/test/15_mrcx.bats b/test/15_mrcx.bats
index 0ac0d17..8519247 100644
--- a/test/15_mrcx.bats
+++ b/test/15_mrcx.bats
@@ -105,3 +105,9 @@ setup () {
   make slices/sjubroder-00450.mrcx
   xmllint --format slices/sjubroder-00450.mrcx | grep -q 'tag="490"'
 }
+
+@test "MARCXML: cleans up bad 260c values" {
+  make slices/suoja-pirtti-00000.mrcx
+  run bash -c "xmllint --format slices/suoja-pirtti-00000.mrcx | grep -A 3 'tag=.260.' | grep 'code=.c.' | grep 'Merkur'"
+  [ "$status" -ne 0 ]
+}