diff --git a/core/trino-main/src/main/java/io/trino/server/protocol/JsonEncodingUtils.java b/core/trino-main/src/main/java/io/trino/server/protocol/JsonEncodingUtils.java
index e8c8970e0a32d..9183bb4fb9cb0 100644
--- a/core/trino-main/src/main/java/io/trino/server/protocol/JsonEncodingUtils.java
+++ b/core/trino-main/src/main/java/io/trino/server/protocol/JsonEncodingUtils.java
@@ -263,7 +263,7 @@ public void encode(JsonGenerator generator, ConnectorSession session, Block bloc
                 return;
             }
             Slice slice = VARCHAR.getSlice(block, position);
-            generator.writeString(slice.toStringUtf8());
+            generator.writeUTF8String(slice.byteArray(), slice.byteArrayOffset(), slice.length());
         }
     }
 
@@ -286,7 +286,7 @@ public void encode(JsonGenerator generator, ConnectorSession session, Block bloc
                 return;
             }
             Slice slice = padSpaces(VARCHAR.getSlice(block, position), length);
-            generator.writeString(slice.toStringUtf8());
+            generator.writeUTF8String(slice.byteArray(), slice.byteArrayOffset(), slice.length());
         }
     }