diff --git a/src/Lean/CoreM.lean b/src/Lean/CoreM.lean
index 4e1d393c8c4b..2eaa92138232 100644
--- a/src/Lean/CoreM.lean
+++ b/src/Lean/CoreM.lean
@@ -309,7 +309,7 @@ register_builtin_option debug.moduleNameAtTimeout : Bool := {
 def throwMaxHeartbeat (moduleName : Name) (optionName : Name) (max : Nat) : CoreM Unit := do
   let includeModuleName := debug.moduleNameAtTimeout.get (← getOptions)
   let atModuleName := if includeModuleName then s!" at `{moduleName}`" else ""
-  throw <| Exception.error (← getRef) m!"\
+  throw <| Exception.error (← getRef) <| .tagged `runtime.maxHeartbeats m!"\
     (deterministic) timeout{atModuleName}, maximum number of heartbeats ({max/1000}) has been reached\n\
     Use `set_option {optionName} <num>` to set the limit.\
     {useDiagnosticMsg}"
@@ -396,8 +396,7 @@ export Core (CoreM mkFreshUserName checkSystem withCurrHeartbeats)
   We used a similar hack at `Exception.isMaxRecDepth` -/
 def Exception.isMaxHeartbeat (ex : Exception) : Bool :=
   match ex with
-  | Exception.error _ (MessageData.ofFormatWithInfos ⟨Std.Format.text msg, _⟩) =>
-    "(deterministic) timeout".isPrefixOf msg
+  | Exception.error _ (.tagged tag _) => (`runtime.maxHeartbeats).isPrefixOf tag
   | _ => false
 
 /-- Creates the expression `d → b` -/