diff --git a/internal/flag/resolution_detail.go b/internal/flag/resolution_detail.go
index 66f50cc8139..d06a0aa36d1 100644
--- a/internal/flag/resolution_detail.go
+++ b/internal/flag/resolution_detail.go
@@ -8,5 +8,5 @@ type ResolutionDetails struct {
 	Reason ResolutionReason
 
 	// ErrorCode indicates the error code for this evaluation
-	ErrorCode string
+	ErrorCode ErrorCode
 }