diff --git a/src/Compiler/Checking/CheckDeclarations.fs b/src/Compiler/Checking/CheckDeclarations.fs
index 0bc7c5e1917..6f9c0a21d53 100644
--- a/src/Compiler/Checking/CheckDeclarations.fs
+++ b/src/Compiler/Checking/CheckDeclarations.fs
@@ -5749,6 +5749,12 @@ let CheckOneImplFile
                 try  
                     let reportErrors = not (checkForErrors())
                     let tcVal = LightweightTcValForUsingInBuildMethodCall g
+                    use _ =
+                        Activity.start "PostTypeCheckSemanticChecks.CheckImplFile"
+                            [|
+                                Activity.Tags.fileName, fileName
+                                Activity.Tags.qualifiedNameOfFile, qualNameOfFile.Text
+                            |]
                     PostTypeCheckSemanticChecks.CheckImplFile 
                        (g, cenv.amap, reportErrors, cenv.infoReader, 
                         env.eInternalsVisibleCompPaths, cenv.thisCcu, tcVal, envAtEnd.DisplayEnv,