diff --git a/src/main/scala/millfork/error/ConsoleLogger.scala b/src/main/scala/millfork/error/ConsoleLogger.scala
index c8860e40..fd7c639a 100644
--- a/src/main/scala/millfork/error/ConsoleLogger.scala
+++ b/src/main/scala/millfork/error/ConsoleLogger.scala
@@ -22,14 +22,17 @@ class ConsoleLogger extends Logger {
   private def printErrorContext(pos: Option[Position]): Unit = synchronized {
     pos.foreach { position =>
         sourceLines.get(position.moduleName).foreach { lines =>
-          val line = lines.apply(pos.get.line - 1)
-          val column = pos.get.column - 1
-          val margin = "       "
-          print(margin)
-          println(line)
-          print(margin)
-          print(" " * column)
-          println("^")
+          val lineIx = pos.get.line - 1
+          if (lineIx < lines.length) {
+            val line = lines.apply(lineIx)
+            val column = pos.get.column - 1
+            val margin = "       "
+            print(margin)
+            println(line)
+            print(margin)
+            print(" " * column)
+            println("^")
+          }
         }
     }
   }
diff --git a/src/test/scala/millfork/test/BasicSymonTest.scala b/src/test/scala/millfork/test/BasicSymonTest.scala
index d8175e05..e1a45b56 100644
--- a/src/test/scala/millfork/test/BasicSymonTest.scala
+++ b/src/test/scala/millfork/test/BasicSymonTest.scala
@@ -147,10 +147,14 @@ class BasicSymonTest extends FunSuite with Matchers {
   test("Segment syntax") {
     EmuUnoptimizedCrossPlatformRun(Cpu.Mos, Cpu.Z80, Cpu.Intel8080, Cpu.Sharp, Cpu.Intel8086, Cpu.Motorola6809)(
       """
-        | segment(default)byte output @$c000
+        | segment ( default ) byte output @$c000
         | segment(default)array x[3]
         | segment(default)void main () {
         | }
+        | segment (default) {
+        |  const byte a = 1
+        |  //
+        | }
       """.stripMargin){ m => () }
   }
 
diff --git a/src/test/scala/millfork/test/ParserSuite.scala b/src/test/scala/millfork/test/ParserSuite.scala
new file mode 100644
index 00000000..c7dabc18
--- /dev/null
+++ b/src/test/scala/millfork/test/ParserSuite.scala
@@ -0,0 +1,56 @@
+package millfork.test
+
+import millfork.Cpu
+import millfork.test.emu.{EmuUnoptimizedCrossPlatformRun, ShouldNotCompile}
+import org.scalatest.{FunSuite, Matchers}
+
+/**
+  * @author Karol Stasiak
+  */
+class ParserSuite extends FunSuite with Matchers  {
+
+  test("Require space between flags and types") {
+    ShouldNotCompile(
+      """
+        | constbyte a = 2
+        |
+      """.stripMargin)
+  }
+
+  test("Comment after last constant") {
+    EmuUnoptimizedCrossPlatformRun(Cpu.Mos, Cpu.Z80, Cpu.Motorola6809)(
+      """
+        |
+        | byte __panic() = 1
+        | const byte x = 5;
+        | const byte a = 2;
+        |
+        |void main () {}//
+        |
+        |
+        |//
+        |
+      """.stripMargin){ m =>
+
+    }
+  }
+
+  test("Allow negation") {
+    EmuUnoptimizedCrossPlatformRun(Cpu.Mos, Cpu.Z80, Cpu.Motorola6809)(
+      """
+        | array output[100] @$c000
+        | const byte x = 5
+        | void main() {
+        | output[0] = -x
+        | output[1] = 0 | (-x)
+        | output[2] = 1 * (-x)
+        | if (x != -x) { output[3] = 5 }
+        | }
+      """.stripMargin){ m =>
+      m.readByte(0xc000) should equal(251)
+      m.readByte(0xc001) should equal(251)
+      m.readByte(0xc002) should equal(251)
+      m.readByte(0xc003) should equal(5)
+    }
+  }
+}