diff --git a/src/main/scala/millfork/env/Environment.scala b/src/main/scala/millfork/env/Environment.scala
index 6b00e54b..2e2b2578 100644
--- a/src/main/scala/millfork/env/Environment.scala
+++ b/src/main/scala/millfork/env/Environment.scala
@@ -1676,10 +1676,13 @@ class Environment(val parent: Option[Environment], val prefix: String, val cpuFa
                   case Some(typ) =>
                     log.error(s"Type $name cannot be used as an array index", l.position)
                     w -> Constant.Zero
-                  case _ => w -> eval(l).getOrElse(errorConstant(s"Array `${stmt.name}` has non-constant length", stmt.position))
+                  case _ =>
+                    val constant = eval(l).getOrElse(errorConstant(s"Array `${stmt.name}` has non-constant length", stmt.position))
+                    w -> constant
                 }
               case _ =>
-                w -> eval(l).getOrElse(errorConstant(s"Array `${stmt.name}` has non-constant length", stmt.position))
+                val constant = eval(l).getOrElse(errorConstant(s"Array `${stmt.name}` has non-constant length", stmt.position))
+                w -> constant
             }
             lengthConst match {
               case NumericConstant(length, _) =>
diff --git a/src/main/scala/millfork/node/opt/UnusedGlobalVariables.scala b/src/main/scala/millfork/node/opt/UnusedGlobalVariables.scala
index dee0ff9c..b2f8bd64 100644
--- a/src/main/scala/millfork/node/opt/UnusedGlobalVariables.scala
+++ b/src/main/scala/millfork/node/opt/UnusedGlobalVariables.scala
@@ -16,7 +16,7 @@ object UnusedGlobalVariables extends NodeOptimization {
       case _ => None
     }.toMap
     val allNonvolatileGlobalVariables = nodes.flatMap {
-      case v: VariableDeclarationStatement => if (v.address.isDefined || v.volatile) Nil else List(v.name)
+      case v: VariableDeclarationStatement => if (v.address.isDefined || v.volatile || v.constant) Nil else List(v.name)
       case v: ArrayDeclarationStatement => if (v.address.isDefined) Nil else List(v.name)
       case _ => Nil
     }.toSet
@@ -50,7 +50,7 @@ object UnusedGlobalVariables extends NodeOptimization {
 
   def getAllReadVariables(expressions: List[Node]): List[String] = expressions.flatMap {
     case s: VariableDeclarationStatement => getAllReadVariables(s.address.toList) ++ getAllReadVariables(s.initialValue.toList) ++ (if (s.stack) List("__sp", "__stack") else Nil)
-    case s: ArrayDeclarationStatement => getAllReadVariables(s.address.toList) ++ getAllReadVariables(s.elements.toList)
+    case s: ArrayDeclarationStatement => getAllReadVariables(s.address.toList) ++ getAllReadVariables(s.length.toList) ++ getAllReadVariables(s.elements.toList)
     case s: ArrayContents => getAllReadVariables(s.getAllExpressions(false)) // endianness doesn't matter here at all
     case s: FunctionDeclarationStatement => getAllReadVariables(s.address.toList) ++ getAllReadVariables(s.statements.getOrElse(Nil))
     case Assignment(VariableExpression(_), expr) => getAllReadVariables(expr :: Nil)
diff --git a/src/test/scala/millfork/test/ConstantSuite.scala b/src/test/scala/millfork/test/ConstantSuite.scala
index 7604a95f..a637e342 100644
--- a/src/test/scala/millfork/test/ConstantSuite.scala
+++ b/src/test/scala/millfork/test/ConstantSuite.scala
@@ -2,7 +2,7 @@ package millfork.test
 
 import millfork.Cpu
 import millfork.env.{BasicPlainType, DerivedPlainType, NumericConstant}
-import millfork.test.emu.{EmuUnoptimizedCrossPlatformRun, EmuUnoptimizedRun, ShouldNotCompile}
+import millfork.test.emu.{EmuBenchmarkRun, EmuOptimizedCmosRun, EmuUnoptimizedCrossPlatformRun, EmuUnoptimizedRun, ShouldNotCompile}
 import org.scalatest.{FunSuite, Matchers}
 
 /**
@@ -130,4 +130,19 @@ class ConstantSuite extends FunSuite with Matchers {
     m.readByte(0xc011) should equal(89)
 
   }
+
+  test("Constant array sizes") {
+    val m = EmuOptimizedCmosRun(
+          """
+            | const byte A = 8
+            | const byte B = 8
+            | const byte SIZE = A * B
+            | array(byte) arr[SIZE] @$c000
+            | void main() {
+            |   arr[0] = 1
+            | }
+            |
+          """.stripMargin)
+    m.readByte(0xc000) should equal(1)
+  }
 }