diff --git a/core/src/main/antlr4/org/evomaster/core/parser/RegexEcma262.g4 b/core/src/main/antlr4/org/evomaster/core/parser/RegexEcma262.g4
index 0aa6ab1ef8..31c720960e 100644
--- a/core/src/main/antlr4/org/evomaster/core/parser/RegexEcma262.g4
+++ b/core/src/main/antlr4/org/evomaster/core/parser/RegexEcma262.g4
@@ -22,7 +22,7 @@ grammar RegexEcma262;
 //------ PARSER ------------------------------
 // Parser rules have first letter in lower-case
 
-pattern : disjunction;
+pattern : disjunction EOF;
 
 
 disjunction
@@ -96,13 +96,13 @@ atom
 
 
 //TODO
-//CharacterEscape
+CharacterEscape
 // : ControlEscape
 // | 'c' ControlLetter
-// | HexEscapeSequence
-// | UnicodeEscapeSequence
+ : HexEscapeSequence
+ | UnicodeEscapeSequence
  //| IdentityEscape
-// ;
+ ;
 
 //TODO
 //ControlEscape
@@ -205,7 +205,7 @@ AtomEscape
  : '\\' CharacterClassEscape
  //TODO
 // | '\\' DecimalEscape
-// | '\\' CharacterEscape
+ | '\\' CharacterEscape
  ;
 
 fragment CharacterClassEscape
@@ -238,11 +238,17 @@ BaseChar
  : ~[0-9,^$\\.*+?()[\]{}|-]
  ;
 
-//TODO
-//HexEscapeSequence
-// : 'x' HexDigit HexDigit
-// ;
-//
+UnicodeEscapeSequence
+ : 'u' HexDigit HexDigit HexDigit HexDigit
+ ;
+
+HexEscapeSequence
+ : 'x' HexDigit HexDigit
+ ;
+
+fragment HexDigit:
+ [a-fA-F0-9]
+ ;
 
 //TODO
 //DecimalIntegerLiteral
diff --git a/core/src/main/antlr4/org/evomaster/core/parser/RegexJava.g4 b/core/src/main/antlr4/org/evomaster/core/parser/RegexJava.g4
index f9641dbec9..47eb5a2296 100644
--- a/core/src/main/antlr4/org/evomaster/core/parser/RegexJava.g4
+++ b/core/src/main/antlr4/org/evomaster/core/parser/RegexJava.g4
@@ -23,7 +23,7 @@ grammar RegexJava;
 //------ PARSER ------------------------------
 // Parser rules have first letter in lower-case
 
-pattern : disjunction;
+pattern : disjunction EOF;
 
 
 disjunction
@@ -119,13 +119,13 @@ quoteChar
 ;
 
 //TODO
-//CharacterEscape
+CharacterEscape
 // : ControlEscape
 // | 'c' ControlLetter
-// | HexEscapeSequence
-// | UnicodeEscapeSequence
+ : HexEscapeSequence
+ | UnicodeEscapeSequence
  //| IdentityEscape
-// ;
+ ;
 
 //TODO
 //ControlEscape
@@ -230,7 +230,7 @@ AtomEscape
  : '\\' CharacterClassEscape
  //TODO
 // | '\\' DecimalEscape
-// | '\\' CharacterEscape
+ | '\\' CharacterEscape
  ;
 
 fragment CharacterClassEscape
@@ -267,11 +267,17 @@ BaseChar
  : ~[0-9,^$\\.*+?()[\]{}|-]
  ;
 
-//TODO
-//HexEscapeSequence
-// : 'x' HexDigit HexDigit
-// ;
-//
+UnicodeEscapeSequence:
+ 'u' HexDigit HexDigit HexDigit HexDigit
+;
+
+HexEscapeSequence
+ : 'x' HexDigit HexDigit
+ ;
+
+fragment HexDigit:
+ [a-fA-F0-9]
+ ;
 
 //TODO
 //DecimalIntegerLiteral
diff --git a/core/src/main/kotlin/org/evomaster/core/parser/GeneRegexEcma262Visitor.kt b/core/src/main/kotlin/org/evomaster/core/parser/GeneRegexEcma262Visitor.kt
index 74cb86749b..3cdb7786cb 100644
--- a/core/src/main/kotlin/org/evomaster/core/parser/GeneRegexEcma262Visitor.kt
+++ b/core/src/main/kotlin/org/evomaster/core/parser/GeneRegexEcma262Visitor.kt
@@ -2,6 +2,7 @@ package org.evomaster.core.parser
 
 import org.evomaster.core.search.gene.regex.*
 
+private const val EOF_TOKEN = "<EOF>"
 /**
  * Parser Visitor based on the RegexEcma262.g4 grammar file
  */
@@ -16,7 +17,8 @@ class GeneRegexEcma262Visitor : RegexEcma262BaseVisitor<VisitResult>(){
 
         val disjList = DisjunctionListRxGene(res.genes.map { it as DisjunctionRxGene })
 
-        val gene = RegexGene("regex", disjList,"${RegexGene.JAVA_REGEX_PREFIX}$text")
+        // we remove the <EOF> token from end of the string to store as sourceRegex
+        val gene = RegexGene("regex", disjList,"${RegexGene.JAVA_REGEX_PREFIX}${text.substring(0,text.length - EOF_TOKEN.length)}")
 
         return VisitResult(gene)
     }
@@ -166,9 +168,22 @@ class GeneRegexEcma262Visitor : RegexEcma262BaseVisitor<VisitResult>(){
             return VisitResult(gene)
         }
 
-        if(ctx.AtomEscape() != null){
-            val char = ctx.AtomEscape().text[1].toString()
-            return VisitResult(CharacterClassEscapeRxGene(char))
+        if(ctx.AtomEscape() != null) {
+            val txt = ctx.AtomEscape().text
+            when {
+                txt[1] == 'x' || txt[1] == 'u' -> {
+                    val hexValue =
+                        txt.subSequence(2, txt.length).toString().toInt(16)
+                    return VisitResult(
+                        PatternCharacterBlockGene(
+                            txt,
+                            hexValue.toChar().toString()
+                        )
+                    )
+                }
+
+                else -> return VisitResult(CharacterClassEscapeRxGene(txt[1].toString()))
+            }
         }
 
         if(ctx.disjunction() != null){
diff --git a/core/src/main/kotlin/org/evomaster/core/parser/GeneRegexJavaVisitor.kt b/core/src/main/kotlin/org/evomaster/core/parser/GeneRegexJavaVisitor.kt
index 2fe1081538..bd25b11714 100644
--- a/core/src/main/kotlin/org/evomaster/core/parser/GeneRegexJavaVisitor.kt
+++ b/core/src/main/kotlin/org/evomaster/core/parser/GeneRegexJavaVisitor.kt
@@ -2,6 +2,7 @@ package org.evomaster.core.parser
 
 import org.evomaster.core.search.gene.regex.*
 
+private const val EOF_TOKEN = "<EOF>"
 /**
  * Created by arcuri82 on 11-Sep-19.
  */
@@ -16,7 +17,8 @@ class GeneRegexJavaVisitor : RegexJavaBaseVisitor<VisitResult>(){
 
         val disjList = DisjunctionListRxGene(res.genes.map { it as DisjunctionRxGene })
 
-        val gene = RegexGene("regex", disjList,"${RegexGene.JAVA_REGEX_PREFIX}$text")
+        // we remove the <EOF> token from end of the string to store as sourceRegex
+        val gene = RegexGene("regex", disjList,"${RegexGene.JAVA_REGEX_PREFIX}${text.substring(0, text.length - EOF_TOKEN.length)}")
 
         return VisitResult(gene)
     }
@@ -179,8 +181,20 @@ class GeneRegexJavaVisitor : RegexJavaBaseVisitor<VisitResult>(){
         }
 
         if(ctx.AtomEscape() != null){
-            val char = ctx.AtomEscape().text[1].toString()
-            return VisitResult(CharacterClassEscapeRxGene(char))
+            val txt = ctx.AtomEscape().text
+            when {
+                txt[1] == 'x' || txt[1] == 'u' -> {
+                    val hexValue =
+                        txt.subSequence(2, txt.length).toString().toInt(16)
+                    return VisitResult(
+                        PatternCharacterBlockGene(
+                            txt,
+                            hexValue.toChar().toString()
+                        )
+                    )
+                }
+                else -> return VisitResult(CharacterClassEscapeRxGene(txt[1].toString()))
+            }
         }
 
         if(ctx.disjunction() != null){
diff --git a/core/src/test/kotlin/org/evomaster/core/parser/GeneRegexEcma262VisitorTest.kt b/core/src/test/kotlin/org/evomaster/core/parser/GeneRegexEcma262VisitorTest.kt
index fbf487d70d..2a906745c9 100644
--- a/core/src/test/kotlin/org/evomaster/core/parser/GeneRegexEcma262VisitorTest.kt
+++ b/core/src/test/kotlin/org/evomaster/core/parser/GeneRegexEcma262VisitorTest.kt
@@ -326,4 +326,14 @@ open class GeneRegexEcma262VisitorTest : RegexTestTemplate(){
         // p = 1 / 2^6 = 1 / 64
         checkCanSample("^((a|A)(b|B)(c|C)123(e|E)(f|F)(d|D))$", "aBc123EFd", 10_000)
     }
+
+    @Test
+    fun testHexEscape(){
+        checkSameAsJava("""\x00\x0a\xba\xFF""")
+    }
+
+    @Test
+    fun testUnicodeEscape(){
+        checkSameAsJava("""\u0000\u0a0b\uffff""")
+    }
 }
\ No newline at end of file
diff --git a/core/src/test/kotlin/org/evomaster/core/parser/RegexHandlerTest.kt b/core/src/test/kotlin/org/evomaster/core/parser/RegexHandlerTest.kt
index 5fd3af1e7d..b77e39c04e 100644
--- a/core/src/test/kotlin/org/evomaster/core/parser/RegexHandlerTest.kt
+++ b/core/src/test/kotlin/org/evomaster/core/parser/RegexHandlerTest.kt
@@ -121,4 +121,15 @@ internal class RegexHandlerTest{
 
     }
 
+    @Test
+    fun testCreateGeneForJVMInvalidRegex() {
+
+        assertThrows(ParseCancellationException::class.java) { RegexHandler.createGeneForJVM("\\xR") }
+    }
+
+    @Test
+    fun testCreateGeneForEcma262InvalidRegex() {
+
+        assertThrows(ParseCancellationException::class.java) { RegexHandler.createGeneForEcma262("\\xR") }
+    }
 }
\ No newline at end of file