src/cmd/link/internal/ld/outbuf.go | 4 +++-

diff --git a/src/cmd/link/internal/ld/outbuf.go b/src/cmd/link/internal/ld/outbuf.go
index 09162ae90f594b7a8361e237e782361be0ce26ed..7bc89540c696e0da5108b19c994a61e0d774974f 100644
--- a/src/cmd/link/internal/ld/outbuf.go
+++ b/src/cmd/link/internal/ld/outbuf.go
@@ -187,7 +187,9 @@ 		}
 		// See if our heap would grow to be too large, and if so, copy it to the end
 		// of the mmapped area.
 		if heapLen > maxOutBufHeapLen && out.copyHeap() {
-			heapPos, heapLen, lenNeeded = 0, 0, lenToWrite
+			heapPos -= heapLen
+			lenNeeded = heapPos + lenToWrite
+			heapLen = 0
 		}
 		out.heap = append(out.heap, make([]byte, lenNeeded-heapLen)...)
 	}