--- a/mercurial/revlog.py	Tue Jun 19 15:03:58 2018 +0200
+++ b/mercurial/revlog.py	Tue Jul 10 15:17:05 2018 -0700
@@ -227,6 +227,10 @@
     endbyte = start(revs[-1]) + length(revs[-1])
     readdata = deltachainspan = endbyte - startbyte
 
+    if deltachainspan < revlog._srmingapsize:
+        yield revs
+        return
+
     chainpayload = sum(length(r) for r in revs)
 
     if deltachainspan: