Index: b/hadrian/hadrian.cabal
===================================================================
--- a/hadrian/hadrian.cabal
+++ b/hadrian/hadrian.cabal
@@ -18,7 +18,7 @@ source-repository head
 -- To accommodate #16873
 flag threaded
     manual:              True
-    default:             True
+    default:             False
     description:         Build with the threaded runtime for improved
                          performance. Users with bootstrap compilers
                          which don't support the threaded runtime should
@@ -177,14 +177,6 @@ executable hadrian
                        -rtsopts
                        -fno-ignore-asserts
 
-    if flag(threaded)
-      ghc-options:
-                       -- * -I0: Disable idle GC to avoid redundant GCs while
-                       --        waiting for external processes
-                       -- * -qg: Don't use parallel GC as the synchronization
-                       --        time tends to eat any benefit.
-                       "-with-rtsopts=-I0 -qg"
-                       -threaded
 
     if flag(selftest)
       other-modules:   Rules.Selftest
