diff --git a/src/core/ddsc/src/dds__types.h b/src/core/ddsc/src/dds__types.h
index 4b4cb03..457a1b9 100644
--- a/src/core/ddsc/src/dds__types.h
+++ b/src/core/ddsc/src/dds__types.h
@@ -247,6 +247,7 @@ typedef struct dds_readcond
   struct
   {
       dds_querycondition_filter_fn m_filter;
+      unsigned m_index; /* index in RHC condition masks */
   } m_query;
 }
 dds_readcond;
diff --git a/src/core/ddsc/src/dds_readcond.c b/src/core/ddsc/src/dds_readcond.c
index 3af397c..503e072 100644
--- a/src/core/ddsc/src/dds_readcond.c
+++ b/src/core/ddsc/src/dds_readcond.c
@@ -45,6 +45,7 @@ dds_create_readcond(
     cond->m_rd_guid = rd->m_entity.m_guid;
     if (kind == DDS_KIND_COND_QUERY) {
         cond->m_query.m_filter = filter;
+        cond->m_query.m_index = UINT_MAX;
     }
     dds_rhc_add_readcondition (cond);
     return cond;
diff --git a/src/core/ddsc/src/dds_rhc.c b/src/core/ddsc/src/dds_rhc.c
index b50fb89..2c704d5 100644
--- a/src/core/ddsc/src/dds_rhc.c
+++ b/src/core/ddsc/src/dds_rhc.c
@@ -152,6 +152,9 @@
    even when generating an invalid sample for an unregister message using
    the tkmap data. */
 
+typedef uint32_t querycond_mask_t;
+#define MAX_ATTACHED_QUERYCONDS (CHAR_BIT * sizeof (querycond_mask_t))
+
 #define TRACE(...) DDS_LOG(DDS_LC_RHC, __VA_ARGS__)
 
 /******************************
@@ -299,6 +302,7 @@ struct rhc
   os_mutex lock;
   dds_readcond * conds;             /* List of associated read conditions */
   uint32_t nconds;                  /* Number of associated read conditions */
+  uint32_t nqconds;                 /* Number of associated query conditions */
 };
 
 struct trigger_info
@@ -2129,17 +2133,20 @@ static uint32_t rhc_get_cond_trigger (struct rhc_instance * const inst, const dd
   return m ? 1 : 0;
 }
 
-void dds_rhc_add_readcondition (dds_readcond * cond)
+void dds_rhc_add_readcondition (dds_readcond *cond)
 {
   /* On the assumption that a readcondition will be attached to a
      waitset for nearly all of its life, we keep track of all
      readconditions on a reader in one set, without distinguishing
      between those attached to a waitset or not. */
 
-  struct rhc * rhc = cond->m_rhc;
+  struct rhc *rhc = cond->m_rhc;
   struct ut_hhIter iter;
   struct rhc_instance * inst;
 
+  assert ((dds_entity_kind (&cond->m_entity) == DDS_KIND_COND_READ && cond->m_query.m_filter == 0) ||
+          (dds_entity_kind (&cond->m_entity) == DDS_KIND_COND_QUERY && cond->m_query.m_filter != 0));
+
   cond->m_qminv = qmask_from_dcpsquery (cond->m_sample_states, cond->m_view_states, cond->m_instance_states);
 
   os_mutexLock (&rhc->lock);
@@ -2153,8 +2160,29 @@ void dds_rhc_add_readcondition (dds_readcond * cond)
       }
     }
   }
+
   cond->m_rhc_next = rhc->conds;
   rhc->nconds++;
+  if (cond->m_query.m_filter)
+  {
+    /* Attaching a query condition means selecting an available index in the bitmasks of matching conditions, clearing the bit in all the masks & evaluating the condition on all samples. For the clearing and the setting of the instance mask, we need to scan all instances, not just the non-empty ones. */
+    dds_readcond *rc;
+    querycond_mask_t inv_qcmask = ~(querycond_mask_t)0;
+    assert (cond->m_query.m_index == UINT_MAX);
+    for (rc = rhc->conds; rc != NULL; rc = rc->m_rhc_next)
+      if (rc->m_query.m_filter != 0)
+      {
+        assert (rc->m_query.m_index < MAX_ATTACHED_QUERYCONDS);
+        inv_qcmask &= ~((querycond_mask_t)1 << rc->m_query.m_index);
+      }
+    if (inv_qcmask == 0) abort (); /* FIXME: must return an error instead of crashing */
+    unsigned index = 0;
+    while (!(inv_qcmask & ((querycond_mask_t)1 << index)))
+      index++;
+    cond->m_query.m_index = index;
+
+    rhc->nqconds++;
+  }
   rhc->conds = cond;
 
   TRACE ("add_readcondition(%p, %x, %x, %x) => %p qminv %x ; rhc %u conds\n",
@@ -2164,31 +2192,20 @@ void dds_rhc_add_readcondition (dds_readcond * cond)
   os_mutexUnlock (&rhc->lock);
 }
 
-void dds_rhc_remove_readcondition (dds_readcond * cond)
+void dds_rhc_remove_readcondition (dds_readcond *cond)
 {
-  struct rhc * rhc = cond->m_rhc;
-  dds_readcond * iter;
-  dds_readcond * prev = NULL;
-
+  struct rhc *rhc = cond->m_rhc;
+  dds_readcond **ptr;
   os_mutexLock (&rhc->lock);
-  iter = rhc->conds;
-  while (iter)
+  ptr = &rhc->conds;
+  while (*ptr != cond)
+    ptr = &(*ptr)->m_rhc_next;
+  *ptr = (*ptr)->m_rhc_next;
+  rhc->nconds--;
+  if (cond->m_query.m_filter)
   {
-    if (iter == cond)
-    {
-      if (prev)
-      {
-        prev->m_rhc_next = iter->m_rhc_next;
-      }
-      else
-      {
-        rhc->conds = iter->m_rhc_next;
-      }
-      rhc->nconds--;
-      break;
-    }
-    prev = iter;
-    iter = iter->m_rhc_next;
+    rhc->nqconds--;
+    cond->m_query.m_index = UINT_MAX;
   }
   os_mutexUnlock (&rhc->lock);
 }