diff --git a/Makefile b/Makefile
index d9bd4cbfb..eacfbcc37 100644
--- a/Makefile
+++ b/Makefile
@@ -92,8 +92,9 @@ STACK ?= stack
 #STACK=stack --with-hpack=hpack-0.20
 
 # --threads=16 sometimes gives "commitAndReleaseBuffer: resource vanished (Broken pipe)" but seems harmless
+# --timeout is sometimes strangely too short with multiple threads, so only used coarsely here to prevent a total hang
 # More threads and/or testing unoptimised builds requires a larger timeout.
-SHELLTESTOPTS=--execdir --threads=16 --timeout=10 --exclude=/_
+SHELLTESTOPTS=--execdir --threads=16 --timeout=30 --exclude=/_
 
 # make sure shelltest is a released version of shelltestrunner
 # run shell tests using the executable specified in tests