diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index e94c879184..b041d4c1fc 100644
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -676,9 +676,7 @@ func mallocgc(size uintptr, typ *_type, needzero bool) unsafe.Pointer {
 	}
 
 	var scanSize uintptr
-	if noscan {
-		heapBitsSetTypeNoScan(uintptr(x))
-	} else {
+	if !noscan {
 		// If allocating a defer+arg block, now that we've picked a malloc size
 		// large enough to hold everything, cut the "asked for" size down to
 		// just the defer header, so that the GC bitmap will record the arg block
diff --git a/src/runtime/mbitmap.go b/src/runtime/mbitmap.go
index 26e511d495..e23c5cf6c9 100644
--- a/src/runtime/mbitmap.go
+++ b/src/runtime/mbitmap.go
@@ -45,6 +45,11 @@
 // not checkmarked, and is the dead encoding.
 // These properties must be preserved when modifying the encoding.
 //
+// The bitmap for noscan spans is not maintained. Code must ensure
+// that an object is scannable before consulting its bitmap by
+// checking either the noscan bit in the span or by consulting its
+// type's information.
+//
 // Checkmarks
 //
 // In a concurrent garbage collector, one worries about failing to mark
@@ -1363,13 +1368,6 @@ Phase4:
 	}
 }
 
-// heapBitsSetTypeNoScan marks x as noscan by setting the first word
-// of x in the heap bitmap to scalar/dead.
-func heapBitsSetTypeNoScan(x uintptr) {
-	h := heapBitsForAddr(uintptr(x))
-	*h.bitp &^= (bitPointer | bitMarked) << h.shift
-}
-
 var debugPtrmask struct {
 	lock mutex
 	data *byte