diff --git a/htlcswitch/hodl/mask_debug.go b/htlcswitch/hodl/mask_debug.go
new file mode 100644
index 00000000..5d5fd065
--- /dev/null
+++ b/htlcswitch/hodl/mask_debug.go
@@ -0,0 +1,44 @@
+// +build debug
+
+package hodl
+
+import (
+	"fmt"
+	"strings"
+)
+
+// DebugBuild signals that this is a debug build.
+const DebugBuild = true
+
+// MaskFromFlags merges a variadic set of Flags into a single Mask.
+func MaskFromFlags(flags ...Flag) Mask {
+	var mask Mask
+	for _, flag := range flags {
+		mask |= Mask(flag)
+	}
+
+	return mask
+}
+
+// Active returns true if the bit corresponding to the flag is set within the
+// mask.
+func (m Mask) Active(flag Flag) bool {
+	return (Flag(m) & flag) > 0
+}
+
+// String returns a human-readable description of all active Flags.
+func (m Mask) String() string {
+	if m == MaskNone {
+		return "hodl.Mask(NONE)"
+	}
+
+	var activeFlags []string
+	for i := uint(0); i < 32; i++ {
+		flag := Flag(1 << i)
+		if m.Active(flag) {
+			activeFlags = append(activeFlags, flag.String())
+		}
+	}
+
+	return fmt.Sprintf("hodl.Mask(%s)", strings.Join(activeFlags, "|"))
+}