diff --git a/nx01-x4o-o2o/src/main/java/org/x4o/o2o/fc18/FourCornerUnicodeImport.java b/nx01-x4o-o2o/src/main/java/org/x4o/o2o/fc18/FourCornerUnicodeImport.java
index 4a70ad3..f098a65 100644
--- a/nx01-x4o-o2o/src/main/java/org/x4o/o2o/fc18/FourCornerUnicodeImport.java
+++ b/nx01-x4o-o2o/src/main/java/org/x4o/o2o/fc18/FourCornerUnicodeImport.java
@@ -183,7 +183,12 @@ public class FourCornerUnicodeImport {
 					continue;
 				}
 			}
-			throw new IllegalArgumentException("Unsupported char: '" + ((char)codePoint) + "' 0x" + Integer.toHexString(codePoint));
+			StringBuilder err = new StringBuilder();
+			err.append("Unsupported char: '");
+			err.appendCodePoint(codePoint);
+			err.append("' 0x");
+			err.append(Integer.toHexString(codePoint));
+			throw new IllegalArgumentException(err.toString());
 		}
 		return result;
 	}