diff --git a/tests/sys/kern/coredump_phnum_test.sh b/tests/sys/kern/coredump_phnum_test.sh
index a39f0a5f9a8f..3c7cd262ccba 100644
--- a/tests/sys/kern/coredump_phnum_test.sh
+++ b/tests/sys/kern/coredump_phnum_test.sh
@@ -45,10 +45,12 @@ coredump_phnum_body()
 	ulimit -c '$(ulimit -c)'
 	sysctl kern.coredump=$(sysctl -n kern.coredump)
 	sysctl kern.corefile='$(sysctl -n kern.corefile)'
+	sysctl kern.compress_user_cores='$(sysctl -n kern.compress_user_cores)'
 EOF
 
 	ulimit -c unlimited
 	sysctl kern.coredump=1
+	sysctl kern.compress_user_cores=0
 	sysctl kern.corefile="$(pwd)/coredump_phnum_helper.core"
 
 	atf_check -s signal:sigabrt "$(atf_get_srcdir)/coredump_phnum_helper"