diff --git a/src/main/java/org/json/JSONTokener.java b/src/main/java/org/json/JSONTokener.java
index b825ee2..4d13f60 100644
--- a/src/main/java/org/json/JSONTokener.java
+++ b/src/main/java/org/json/JSONTokener.java
@@ -297,45 +297,48 @@ public class JSONTokener {
         for (;;) {
             c = this.next();
             switch (c) {
-                case 0:
-                case '\n':
-                case '\r':
-                    throw this.syntaxError("Unterminated string");
-                case '\\':
-                    c = this.next();
-                    switch (c) {
-                        case 'b':
-                            sb.append('\b');
-                            break;
-                        case 't':
-                            sb.append('\t');
-                            break;
-                        case 'n':
-                            sb.append('\n');
-                            break;
-                        case 'f':
-                            sb.append('\f');
-                            break;
-                        case 'r':
-                            sb.append('\r');
-                            break;
-                        case 'u':
-                            try {
-                                sb.append((char) Integer.parseInt(this.next(4), 16));
-                            } catch (NumberFormatException e) {
-                                throw this.syntaxError("Illegal escape.", e);
-                            }
-                            break;
-                        case '"':
-                        case '\'':
-                        case '\\':
-                        case '/':
-                            sb.append(c);
-                            break;
-                        default:
-                            throw this.syntaxError("Illegal escape.");
+            case 0:
+            case '\n':
+            case '\r':
+                throw this.syntaxError("Unterminated string. " +
+                        "Character with int code " + (int) c + " is not allowed within a quoted string.");
+            case '\\':
+                c = this.next();
+                switch (c) {
+                case 'b':
+                    sb.append('\b');
+                    break;
+                case 't':
+                    sb.append('\t');
+                    break;
+                case 'n':
+                    sb.append('\n');
+                    break;
+                case 'f':
+                    sb.append('\f');
+                    break;
+                case 'r':
+                    sb.append('\r');
+                    break;
+                case 'u':
+                    String next = this.next(4);
+                    try {
+                        sb.append((char)Integer.parseInt(next, 16));
+                    } catch (NumberFormatException e) {
+                        throw this.syntaxError("Illegal escape. " +
+                                "\\u must be followed by a 4 digit hexadecimal number. \\" + next + " is not valid.", e);
                     }
                     break;
+                case '"':
+                case '\'':
+                case '\\':
+                case '/':
+                    sb.append(c);
+                    break;
+                default:
+                    throw this.syntaxError("Illegal escape. Escape sequence  \\" + c + " is not valid.");
+                }
+                break;
                 default:
                     if (strictMode && c == '\"' && quote != c) {
                         throw this.syntaxError(String.format(
diff --git a/src/test/java/org/json/junit/JSONObjectTest.java b/src/test/java/org/json/junit/JSONObjectTest.java
index fac8c53..a8b25eb 100644
--- a/src/test/java/org/json/junit/JSONObjectTest.java
+++ b/src/test/java/org/json/junit/JSONObjectTest.java
@@ -2193,6 +2193,60 @@ public class JSONObjectTest {
         }
     }
 
+    @Test
+    public void jsonObjectParseControlCharacterEOFAssertExceptionMessage(){
+        char c = '\0';
+        final String source = "{\"key\":\"" + c + "\"}";
+        try {
+            JSONObject jo = new JSONObject(source);
+            fail("JSONException should be thrown");
+        } catch (JSONException ex) {
+            assertEquals("Unterminated string. " + "Character with int code 0" +
+                    " is not allowed within a quoted string. at 8 [character 9 line 1]", ex.getMessage());
+        }
+    }
+
+    @Test
+    public void jsonObjectParseControlCharacterNewLineAssertExceptionMessage(){
+        char[] chars = {'\n', '\r'};
+        for( char c : chars) {
+            final String source = "{\"key\":\"" + c + "\"}";
+            try {
+                JSONObject jo = new JSONObject(source);
+                fail("JSONException should be thrown");
+            } catch (JSONException ex) {
+                assertEquals("Unterminated string. " + "Character with int code " + (int) c +
+                        " is not allowed within a quoted string. at 9 [character 0 line 2]", ex.getMessage());
+            }
+        }
+    }
+
+    @Test
+    public void jsonObjectParseUTF8EncodingAssertExceptionMessage(){
+        String c = "\\u123x";
+        final String source = "{\"key\":\"" + c + "\"}";
+        try {
+            JSONObject jo = new JSONObject(source);
+            fail("JSONException should be thrown");
+        } catch (JSONException ex) {
+            assertEquals("Illegal escape. \\u must be followed by a 4 digit hexadecimal number. " +
+                    "\\123x is not valid. at 14 [character 15 line 1]", ex.getMessage());
+        }
+    }
+
+    @Test
+    public void jsonObjectParseIllegalEscapeAssertExceptionMessage(){
+        String c = "\\x";
+        final String source = "{\"key\":\"" + c + "\"}";
+        try {
+            JSONObject jo = new JSONObject(source);
+            fail("JSONException should be thrown");
+        } catch (JSONException ex) {
+            assertEquals("Illegal escape. Escape sequence  " + c + " is not valid." +
+                    " at 10 [character 11 line 1]", ex.getMessage());
+        }
+    }
+
     /**
      * Explore how JSONObject handles parsing errors.
      */
diff --git a/src/test/java/org/json/junit/JSONParserConfigurationTest.java b/src/test/java/org/json/junit/JSONParserConfigurationTest.java
index 1ce289e..a1838a4 100644
--- a/src/test/java/org/json/junit/JSONParserConfigurationTest.java
+++ b/src/test/java/org/json/junit/JSONParserConfigurationTest.java
@@ -164,7 +164,7 @@ public class JSONParserConfigurationTest {
             () -> new JSONArray(testCaseTwo, jsonParserConfiguration));
 
         assertEquals("Expected a ',' or ']' at 10 [character 11 line 1]", jeOne.getMessage());
-        assertEquals("Unterminated string at 15 [character 16 line 1]", jeTwo.getMessage());
+        assertEquals("Unterminated string. Character with int code 0 is not allowed within a quoted string. at 15 [character 16 line 1]", jeTwo.getMessage());
     }