diff --git a/src/org/joni/ast/StringNode.java b/src/org/joni/ast/StringNode.java
index 4a3c27b..57e87cc 100644
--- a/src/org/joni/ast/StringNode.java
+++ b/src/org/joni/ast/StringNode.java
@@ -22,6 +22,8 @@
 import org.jcodings.Encoding;
 import org.joni.Config;
 import org.joni.constants.internal.StringType;
+import org.joni.exception.ErrorMessages;
+import org.joni.exception.ValueException;
 
 public final class StringNode extends Node implements StringType {
     private static final int NODE_STR_MARGIN = 16;
@@ -138,7 +140,14 @@ public void catByte(byte c) {
 
     public void catCode(int code, Encoding enc) {
         modifyEnsure(Config.ENC_CODE_TO_MBC_MAXLEN);
+        int oldEnd = end;
         end += enc.codeToMbc(code, bytes, end);
+        if (enc.length(bytes, oldEnd, end) < 0) {
+           throw new ValueException(ErrorMessages.ERR_INVALID_UNICODE, code <= 0xFFFF 
+              ? String.format("\\\\u%04X", code) 
+              : String.format("\\\\u%04X\\\\u%04X", Character.highSurrogate(code), Character.lowSurrogate(code))
+           );
+       }
     }
 
     public void setRaw() {
diff --git a/src/org/joni/exception/ErrorMessages.java b/src/org/joni/exception/ErrorMessages.java
index b80340b..4d3cace 100644
--- a/src/org/joni/exception/ErrorMessages.java
+++ b/src/org/joni/exception/ErrorMessages.java
@@ -85,5 +85,6 @@ public interface ErrorMessages extends org.jcodings.exception.ErrorMessages {
     String INVALID_COMBINATION_OF_OPTIONS = "invalid combination of options";
     String OVER_THREAD_PASS_LIMIT_COUNT = "over thread pass limit count";
     String TOO_BIG_SB_CHAR_VALUE = "too big singlebyte char value";
+    String ERR_INVALID_UNICODE = "invalid unicode: %n";
 
 }
diff --git a/test/org/joni/test/TestInvalidUnicode.java b/test/org/joni/test/TestInvalidUnicode.java
new file mode 100644
index 0000000..aac14bf
--- /dev/null
+++ b/test/org/joni/test/TestInvalidUnicode.java
@@ -0,0 +1,54 @@
+/*
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to
+ * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+ * of the Software, and to permit persons to whom the Software is furnished to do
+ * so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package org.joni.test;
+
+import org.jcodings.Encoding;
+import org.jcodings.specific.UTF8Encoding;
+import org.joni.Option;
+import org.joni.Syntax;
+
+public class TestInvalidUnicode extends Test {
+
+   @Override
+   public int option() {
+      return Option.DEFAULT;
+   }
+
+   @Override
+   public Encoding encoding() {
+      return UTF8Encoding.INSTANCE;
+   }
+
+   @Override
+   public String testEncoding() {
+      return "utf-8";
+   }
+
+   @Override
+   public Syntax syntax() {
+      return Syntax.Java;
+   }
+
+   @Override
+   public void test() throws Exception {
+      // see https://github.com/jruby/joni/issues/17
+      xerrs("A\\uD800", "invalid unicode: \\uD800");
+   }
+}