diff --git a/src/main/java/org/codehaus/groovy/runtime/EncodingGroovyMethods.java b/src/main/java/org/codehaus/groovy/runtime/EncodingGroovyMethods.java
index 816df786b36..b49f180fb9f 100644
--- a/src/main/java/org/codehaus/groovy/runtime/EncodingGroovyMethods.java
+++ b/src/main/java/org/codehaus/groovy/runtime/EncodingGroovyMethods.java
@@ -372,12 +372,19 @@ public static byte[] decodeHex(final String value) {
 
         byte[] bytes = new byte[value.length() / 2];
         for (int i = 0; i < value.length(); i += 2) {
-            bytes[i / 2] = (byte) Integer.parseInt(value.substring(i, i + 2), 16);
+            bytes[i / 2] = (byte) ((hexToNibble(value.charAt(i)) << 4) | hexToNibble(value.charAt(i + 1)));
         }
 
         return bytes;
     }
 
+    private static int hexToNibble(final char c) {
+        if (c >= '0' && c <= '9') return c - '0';
+        if (c >= 'A' && c <= 'F') return c - 'A' + 10;
+        if (c >= 'a' && c <= 'f') return c - 'a' + 10;
+        throw new NumberFormatException("illegal hexadecimal character " + c + " in hex string");
+    }
+
     /**
      * Calculate md5 of the CharSequence instance
      * @return md5 value
diff --git a/src/test/groovy/groovy/HexTest.groovy b/src/test/groovy/groovy/HexTest.groovy
index 2e90fe88fe8..a881440158c 100644
--- a/src/test/groovy/groovy/HexTest.groovy
+++ b/src/test/groovy/groovy/HexTest.groovy
@@ -67,6 +67,19 @@ class HexTest {
             "1g".decodeHex()
         }
 
+        // a leading sign is not a valid hexadecimal character and must be rejected
+        // (Integer.parseInt would otherwise accept it and decode a wrong byte)
+        ["-1", "+a", "-f", "+0"].each { bad ->
+            shouldFail(NumberFormatException) {
+                bad.decodeHex()
+            }
+        }
+
+        // non-ASCII digit characters are not valid hexadecimal either
+        shouldFail(NumberFormatException) {
+            "１１".decodeHex()
+        }
+
         // test to make sure a leading zero is handled correctly
         bytes = "0a".decodeHex()
         assert bytes.length == 1