diff --git a/Sources/GRPCOTelTracingInterceptors/Tracing/SpanAttributes+GRPCTracingKeys.swift b/Sources/GRPCOTelTracingInterceptors/Tracing/SpanAttributes+GRPCTracingKeys.swift
index 23a5296..d4a9d64 100644
--- a/Sources/GRPCOTelTracingInterceptors/Tracing/SpanAttributes+GRPCTracingKeys.swift
+++ b/Sources/GRPCOTelTracingInterceptors/Tracing/SpanAttributes+GRPCTracingKeys.swift
@@ -212,7 +212,7 @@ extension Int {
         // non-digit character
         return nil
       }
-      value &+= Int(utf8Char - UInt8(ascii: "0"))
+      value &+= Int(utf8Char &- UInt8(ascii: "0"))
     }
 
     guard value <= Int(UInt16.max) else {