diff --git a/Changes b/Changes
index 185fd0f..38072b5 100644
--- a/Changes
+++ b/Changes
@@ -1,5 +1,7 @@
-0.61.3 2023-07-11
+0.61.3 2023-07-17
     - Add totalResources to results (diewald)
+    - [bugfix] Fix casefolding for case-insensitive queries
+      (diewald).
 
 0.61.2 2023-04-05
     - [bugfix] Fix pagebreak retrieval (margaretha, diewald)
diff --git a/src/main/java/de/ids_mannheim/korap/KrillQuery.java b/src/main/java/de/ids_mannheim/korap/KrillQuery.java
index c10d93c..6729521 100644
--- a/src/main/java/de/ids_mannheim/korap/KrillQuery.java
+++ b/src/main/java/de/ids_mannheim/korap/KrillQuery.java
@@ -1309,7 +1309,22 @@
             value.setLength(offset);
 
             // Add key to value
-            value.append(isCaseInsensitive ? key.toLowerCase() : key);
+
+            if (isCaseInsensitive) {
+
+                // This supports both legacy search and locale-dependent case-folding.
+                // It mimics the Perl fc behaviour probably better than icu4j.
+                if (key.toLowerCase().equals(key.toUpperCase().toLowerCase())) {
+                    value.append(key.toLowerCase());
+                } else {
+                    value.append(key.toLowerCase());
+                    values.push(value.toString());
+                    value.setLength(offset);
+                    value.append(key.toUpperCase().toLowerCase());
+                };
+            } else {
+                value.append(key);
+            };
 
             // TODO:
             //   This should iterate over all values as well
diff --git a/src/test/java/de/ids_mannheim/korap/search/TestKrill.java b/src/test/java/de/ids_mannheim/korap/search/TestKrill.java
index f36cc28..168b83d 100644
--- a/src/test/java/de/ids_mannheim/korap/search/TestKrill.java
+++ b/src/test/java/de/ids_mannheim/korap/search/TestKrill.java
@@ -154,6 +154,34 @@
         assertTrue(res.at("/matches/0/snippet").isMissingNode());
         assertEquals("dem", res.at("/matches/0/tokens/left/0").asText());
         assertEquals("Buchstaben", res.at("/matches/0/tokens/match/0").asText());
+
+        // The test-data is old and therefore precedes the correct testfolding.
+        // However, we can check the correct behaviour nonetheless.
+        String json = "{\"query\":{\"@type\":\"koral:token\",\"wrap\":{\"@type\":\"koral:term\",\"flags\": [\"flags:caseInsensitive\"],\"key\": \"Grösstenteils\",\"layer\":\"orth\",\"match\": \"match:eq\"}}}";
+
+        ObjectMapper mapper = new ObjectMapper();
+
+        ks = new Krill(json);
+        kr = ks.apply(ki);
+        assertEquals(kr.getTotalResults(), 0);
+        assertEquals(kr.getItemsPerPage(), 25);
+        assertEquals(kr.getMatches().size(), 0);
+
+        res = mapper.readTree(kr.toJsonString());
+        assertEquals(res.at("/meta/serialQuery").asText(),"tokens:i:grösstenteils");
+
+        json = "{\"query\":{\"@type\":\"koral:token\",\"wrap\":{\"@type\":\"koral:term\",\"flags\": [\"flags:caseInsensitive\"],\"key\": \"Größtenteils\",\"layer\":\"orth\",\"match\": \"match:eq\"}}}";
+        
+        ks = new Krill(json);
+        kr = ks.apply(ki);
+
+        assertEquals(kr.getTotalResults(), 2);
+        assertEquals(kr.getItemsPerPage(), 25);
+        assertEquals(kr.getMatches().size(), 2);
+
+        res = mapper.readTree(kr.toJsonString());
+        assertEquals(res.at("/meta/serialQuery").asText(),
+                     "spanOr([tokens:i:grösstenteils, tokens:i:größtenteils])");
     };