diff --git a/src/builtins.ts b/src/builtins.ts
index d63064c4..d90d70fa 100644
--- a/src/builtins.ts
+++ b/src/builtins.ts
@@ -3444,7 +3444,7 @@ function evaluateConstantOffset(compiler: Compiler, expression: Expression): i32
       (value = getConstValueI64Low(expr)) < 0
     ) {
       compiler.error(
-        DiagnosticCode.Operation_not_supported,
+        DiagnosticCode.Expression_must_be_a_compile_time_constant,
         expression.range
       );
       value = -1;
@@ -3457,7 +3457,7 @@ function evaluateConstantOffset(compiler: Compiler, expression: Expression): i32
       (value = getConstValueI32(expr)) < 0
     ) {
       compiler.error(
-        DiagnosticCode.Operation_not_supported,
+        DiagnosticCode.Expression_must_be_a_compile_time_constant,
         expression.range
       );
       value = -1;
diff --git a/src/diagnosticMessages.generated.ts b/src/diagnosticMessages.generated.ts
index 831dc9a4..726de9f3 100644
--- a/src/diagnosticMessages.generated.ts
+++ b/src/diagnosticMessages.generated.ts
@@ -30,6 +30,7 @@ export enum DiagnosticCode {
   Function_0_cannot_be_inlined_into_itself = 217,
   Cannot_access_method_0_without_calling_it_as_it_requires_this_to_be_set = 218,
   Optional_properties_are_not_supported = 219,
+  Expression_must_be_a_compile_time_constant = 220,
   Unterminated_string_literal = 1002,
   Identifier_expected = 1003,
   _0_expected = 1005,
@@ -159,6 +160,7 @@ export function diagnosticCodeToString(code: DiagnosticCode): string {
     case 217: return "Function '{0}' cannot be inlined into itself.";
     case 218: return "Cannot access method '{0}' without calling it as it requires 'this' to be set.";
     case 219: return "Optional properties are not supported.";
+    case 220: return "Expression must be a compile-time constant.";
     case 1002: return "Unterminated string literal.";
     case 1003: return "Identifier expected.";
     case 1005: return "'{0}' expected.";
diff --git a/src/diagnosticMessages.json b/src/diagnosticMessages.json
index c1830de6..50d880e6 100644
--- a/src/diagnosticMessages.json
+++ b/src/diagnosticMessages.json
@@ -22,6 +22,7 @@
   "Function '{0}' cannot be inlined into itself.": 217,
   "Cannot access method '{0}' without calling it as it requires 'this' to be set.": 218,
   "Optional properties are not supported.": 219,
+  "Expression must be a compile-time constant.": 220,
 
   "Unterminated string literal.": 1002,
   "Identifier expected.": 1003,