diff --git a/codeOptimizers/src/prog8/optimizer/ConstantIdentifierReplacer.kt b/codeOptimizers/src/prog8/optimizer/ConstantIdentifierReplacer.kt
index 8cf4d5aa1..3324100c7 100644
--- a/codeOptimizers/src/prog8/optimizer/ConstantIdentifierReplacer.kt
+++ b/codeOptimizers/src/prog8/optimizer/ConstantIdentifierReplacer.kt
@@ -87,6 +87,10 @@ internal class ConstantIdentifierReplacer(private val program: Program, private
         if(forloop!=null && identifier===forloop.loopVar)
             return noModifications
 
+        val dt = identifier.inferType(program)
+        if(!dt.isKnown || !dt.isNumeric)
+            return noModifications
+
         try {
             val cval = identifier.constValue(program) ?: return noModifications
             return when (cval.type) {
diff --git a/compiler/test/TestAstChecks.kt b/compiler/test/TestAstChecks.kt
index bbc3c8eb7..a7fd01e32 100644
--- a/compiler/test/TestAstChecks.kt
+++ b/compiler/test/TestAstChecks.kt
@@ -96,4 +96,20 @@ class TestAstChecks: FunSpec({
             """
         compileText(C64Target(), false, text, writeAssembly = false) shouldNotBe null
     }
+
+    test("const is not allowed on arrays") {
+        val text = """
+            main {
+                sub start() {
+                    const ubyte[5] a = 5
+                    a[2]=42
+                }
+            }
+        """
+        val errors = ErrorReporterForTests(keepMessagesAfterReporting = true)
+        compileText(C64Target(), true, text, writeAssembly = true, errors=errors)
+        errors.errors.size shouldBe 1
+        errors.warnings.size shouldBe 0
+        errors.errors[0] shouldContain "const modifier can only be used"
+    }
 })