diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index 6f150f65c9d..8319ac38949 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -202,6 +202,8 @@ Improvements
 * GITHUB#13087: Changed `static final Set` constants to be immutable. Among others it affected
   ScandinavianNormalizer.ALL_FOLDINGS set with public access. (Dmitry Cherniachenko)
 
+* GITHUB#13155: Hunspell: allow ignoring exceptions on duplicate ICONV/OCONV mappings (Peter Gromov)
+
 Optimizations
 ---------------------
 
diff --git a/lucene/analysis/common/src/java/org/apache/lucene/analysis/hunspell/Dictionary.java b/lucene/analysis/common/src/java/org/apache/lucene/analysis/hunspell/Dictionary.java
index 300cf5305d6..5a01a39d3c6 100644
--- a/lucene/analysis/common/src/java/org/apache/lucene/analysis/hunspell/Dictionary.java
+++ b/lucene/analysis/common/src/java/org/apache/lucene/analysis/hunspell/Dictionary.java
@@ -815,7 +815,7 @@ public class Dictionary {
 
     for (int i = 0; i < num; i++) {
       String[] parts = splitBySpace(reader, reader.readLine(), 3);
-      if (mappings.put(parts[1], parts[2]) != null) {
+      if (mappings.put(parts[1], parts[2]) != null && !tolerateDuplicateConversionMappings()) {
         throw new IllegalStateException("duplicate mapping specified for: " + parts[1]);
       }
     }
@@ -1167,6 +1167,14 @@ public class Dictionary {
     return false;
   }
 
+  /**
+   * Whether duplicate ICONV/OCONV lines should be silently ignored. False by default: an {@link
+   * IllegalStateException} will happen.
+   */
+  protected boolean tolerateDuplicateConversionMappings() {
+    return false;
+  }
+
   char[] allNonSuggestibleFlags() {
     return Dictionary.toSortedCharArray(
         Stream.of(HIDDEN_FLAG, noSuggest, forbiddenword, onlyincompound, subStandard)
diff --git a/lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/TestDictionary.java b/lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/TestDictionary.java
index f08fbfbd2d6..28cfb1330ed 100644
--- a/lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/TestDictionary.java
+++ b/lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/TestDictionary.java
@@ -206,6 +206,11 @@ public class TestDictionary extends LuceneTestCase {
         protected boolean tolerateAffixRuleCountMismatches() {
           return true;
         }
+
+        @Override
+        protected boolean tolerateDuplicateConversionMappings() {
+          return true;
+        }
       };
     }
   }
diff --git a/lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/forgivable-errors.aff b/lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/forgivable-errors.aff
index b9b56cc5d65..cb093496691 100644
--- a/lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/forgivable-errors.aff
+++ b/lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/forgivable-errors.aff
@@ -12,4 +12,8 @@ MAP a b
 
 SFX A Y 1
 SFX A   nout        l          [aeiouyáéíóúýůěr][^aeiouyáéíóúýůěrl][^aeiouy
-SFX A b c d
\ No newline at end of file
+SFX A b c d
+
+ICONV 2
+ICONV x y
+ICONV x y
\ No newline at end of file