diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 019f995..b78f2a1 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -26,7 +26,7 @@ jobs:
             cpu: amd64
           #- os: windows
             #cpu: i386
-        branch: [version-1-2, version-1-4, version-1-6, devel]
+        branch: [version-1-6, version-2-0, devel]
         include:
           - target:
               os: linux
diff --git a/chronos.nimble b/chronos.nimble
index 6483d84..6b4ac58 100644
--- a/chronos.nimble
+++ b/chronos.nimble
@@ -36,8 +36,10 @@ task test, "Run all tests":
       "-d:debug -d:chronosPreviewV4",
       "-d:debug -d:chronosDebug -d:useSysAssert -d:useGcAssert",
       "-d:release",
-      "-d:release -d:chronosPreviewV4",
-    ]: run args, "tests/testall"
+      "-d:release -d:chronosPreviewV4"]:
+    run args, "tests/testall"
+    if (NimMajor, NimMinor) > (1, 6):
+      run args & " --mm:refc", "tests/testall"
 
 task test_libbacktrace, "test with libbacktrace":
   var allArgs = @[