diff --git a/src/runtime/mheap.go b/src/runtime/mheap.go
index 6f7dc6eaa6..2c7bfd8a59 100644
--- a/src/runtime/mheap.go
+++ b/src/runtime/mheap.go
@@ -1283,9 +1283,10 @@ HaveSpan:
 	// Publish the span in various locations.
 
 	// This is safe to call without the lock held because the slots
-	// related to this span will only every be read or modified by
-	// this thread until pointers into the span are published or
-	// pageInUse is updated.
+	// related to this span will only ever be read or modified by
+	// this thread until pointers into the span are published (and
+	// we execute a publication barrier at the end of this function
+	// before that happens) or pageInUse is updated.
 	h.setSpans(s.base(), npages, s)
 
 	if !manual {
@@ -1315,6 +1316,11 @@ HaveSpan:
 			traceHeapAlloc()
 		}
 	}
+
+	// Make sure the newly allocated span will be observed
+	// by the GC before pointers into the span are published.
+	publicationBarrier()
+
 	return s
 }