diff --git a/spa/include/spa/props.h b/spa/include/spa/props.h
index a6421a617..4aec84102 100644
--- a/spa/include/spa/props.h
+++ b/spa/include/spa/props.h
@@ -139,6 +139,14 @@ typedef struct {
   const char              **tags;
 } SpaPropInfo;
 
+/**
+ * SpaPropValue:
+ * @type: a property type
+ * @size: the property size
+ * @value: the property value.
+ *
+ * The structure to set and get properties.
+ */
 typedef struct {
   SpaPropType  type;
   size_t       size;
@@ -150,7 +158,10 @@ typedef struct {
  * @n_prop_info: number of elements in @prop_info
  * @prop_info: array of #SpaPropInfo. Contains info about the
  *             properties. Can be %NULL when unspecified.
- * @unset_mask: mask of unset properties
+ * @unset_mask: mask of unset properties. For each property in @prop_info there
+ *              is a corresponding bit that specifies if the property is currently
+ *              unset. When more that 32 properties are present, more uint32_t
+ *              fields follow this one.
  *
  * Generic propertiers.
  */
@@ -160,6 +171,10 @@ struct _SpaProps {
   uint32_t           unset_mask;
 };
 
+#define SPA_PROPS_INDEX_IS_UNSET(p,idx) ((&(p)->unset_mask)[(idx) >> 5] & (1U << ((idx) & 31)))
+#define SPA_PROPS_INDEX_UNSET(p,idx)    ((&(p)->unset_mask)[(idx) >> 5] |= (1U << ((idx) & 31)))
+#define SPA_PROPS_INDEX_SET(p,idx)      ((&(p)->unset_mask)[(idx) >> 5] &= ~(1U << ((idx) & 31)))
+
 static inline unsigned int
 spa_props_index_for_id (const SpaProps *props, uint32_t id)
 {
diff --git a/spa/lib/props.c b/spa/lib/props.c
index 9dc331097..2853d4c3d 100644
--- a/spa/lib/props.c
+++ b/spa/lib/props.c
@@ -46,7 +46,7 @@ spa_props_set_prop (SpaProps           *props,
 
   memcpy (SPA_MEMBER (props, info->offset, void), value->value, value->size);
 
-  props->unset_mask &= ~(1u << index);
+  SPA_PROPS_INDEX_SET (props, index);
 
   return SPA_RESULT_OK;
 }
@@ -68,7 +68,7 @@ spa_props_get_prop (const SpaProps *props,
   if ((info->flags & SPA_PROP_FLAG_READABLE) == 0)
     return SPA_RESULT_INVALID_PROPERTY_ACCESS;
 
-  if (props->unset_mask & (1u << index))
+  if (SPA_PROPS_INDEX_IS_UNSET (props, index))
     return SPA_RESULT_PROPERTY_UNSET;
 
   value->type = info->type;
@@ -103,7 +103,7 @@ spa_props_copy (const SpaProps *src,
 
     memcpy (SPA_MEMBER (dest, info->offset, void), value.value, value.size);
 
-    dest->unset_mask &= ~(1u << i);
+    SPA_PROPS_INDEX_SET (dest, i);
   }
   return SPA_RESULT_OK;
 }