diff --git a/src/main/java/de/neemann/digital/analyse/parser/Parser.java b/src/main/java/de/neemann/digital/analyse/parser/Parser.java
index f735aff56..b2c225f4e 100644
--- a/src/main/java/de/neemann/digital/analyse/parser/Parser.java
+++ b/src/main/java/de/neemann/digital/analyse/parser/Parser.java
@@ -1,9 +1,6 @@
 package de.neemann.digital.analyse.parser;
 
-import de.neemann.digital.analyse.expression.Expression;
-import de.neemann.digital.analyse.expression.Not;
-import de.neemann.digital.analyse.expression.Operation;
-import de.neemann.digital.analyse.expression.Variable;
+import de.neemann.digital.analyse.expression.*;
 import de.neemann.digital.lang.Lang;
 
 import java.io.IOException;
@@ -82,6 +79,10 @@ public class Parser {
                 return exp;
             case IDENT:
                 return new Variable(tokenizer.getIdent());
+            case ONE:
+                return Constant.ONE;
+            case ZERO:
+                return Constant.ZERO;
             default:
                 throw new ParseException(Lang.get("err_parserUnexpectedToken_N", tokenizer.toString()));
         }
diff --git a/src/main/java/de/neemann/digital/analyse/parser/Tokenizer.java b/src/main/java/de/neemann/digital/analyse/parser/Tokenizer.java
index c07eff250..3e79c41fe 100644
--- a/src/main/java/de/neemann/digital/analyse/parser/Tokenizer.java
+++ b/src/main/java/de/neemann/digital/analyse/parser/Tokenizer.java
@@ -11,7 +11,7 @@ import java.io.Reader;
 public class Tokenizer {
 
 
-    enum Token {UNKNOWN, IDENT, AND, OR, NOT, OPEN, CLOSE, EOF}
+    enum Token {UNKNOWN, IDENT, AND, OR, NOT, OPEN, CLOSE, ONE, ZERO, EOF}
 
     private final Reader in;
     private Token token;
@@ -64,6 +64,12 @@ public class Tokenizer {
             case -1:
                 token = Token.EOF;
                 break;
+            case '0':
+                token = Token.ZERO;
+                break;
+            case '1':
+                token = Token.ONE;
+                break;
             case '(':
                 token = Token.OPEN;
                 break;
diff --git a/src/test/java/de/neemann/digital/analyse/parser/ParserTest.java b/src/test/java/de/neemann/digital/analyse/parser/ParserTest.java
index 8090af171..6d68acd3c 100644
--- a/src/test/java/de/neemann/digital/analyse/parser/ParserTest.java
+++ b/src/test/java/de/neemann/digital/analyse/parser/ParserTest.java
@@ -1,9 +1,6 @@
 package de.neemann.digital.analyse.parser;
 
-import de.neemann.digital.analyse.expression.Expression;
-import de.neemann.digital.analyse.expression.Not;
-import de.neemann.digital.analyse.expression.Operation;
-import de.neemann.digital.analyse.expression.Variable;
+import de.neemann.digital.analyse.expression.*;
 import de.neemann.digital.analyse.quinemc.QuineMcCluskey;
 import junit.framework.TestCase;
 
@@ -20,6 +17,11 @@ public class ParserTest extends TestCase {
         assertEquals(new Variable("A^1"), new Parser("A^1").parse());
     }
 
+    public void testConst() throws Exception {
+        assertEquals(Constant.ZERO, new Parser("0").parse());
+        assertEquals(Constant.ONE, new Parser("1").parse());
+    }
+
     public void testParseOr() throws Exception {
         assertTrue(new Parser("a+b").parse() instanceof Operation.Or);
         assertTrue(new Parser("a∨b").parse() instanceof Operation.Or);