diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go
index 85130bf..7f47044 100644
--- a/src/runtime/mgcmark.go
+++ b/src/runtime/mgcmark.go
@@ -415,6 +415,10 @@
 		return
 	}
 
+	if trace.enabled {
+		traceGCMarkAssistStart()
+	}
+
 retry:
 	// Compute the amount of scan work we need to do to make the
 	// balance positive. When the required amount of work is low,
@@ -450,6 +454,9 @@
 		if scanWork == 0 {
 			// We were able to steal all of the credit we
 			// needed.
+			if trace.enabled {
+				traceGCMarkAssistDone()
+			}
 			return
 		}
 	}
@@ -496,6 +503,9 @@
 		// At this point either background GC has satisfied
 		// this G's assist debt, or the GC cycle is over.
 	}
+	if trace.enabled {
+		traceGCMarkAssistDone()
+	}
 }
 
 // gcAssistAlloc1 is the part of gcAssistAlloc that runs on the system