diff --git a/src/backend/storage/lmgr/condition_variable.c b/src/backend/storage/lmgr/condition_variable.c
index 0639689..1acda3c 100644
--- a/src/backend/storage/lmgr/condition_variable.c
+++ b/src/backend/storage/lmgr/condition_variable.c
@@ -61,7 +61,8 @@ ConditionVariablePrepareToSleep(ConditionVariable *cv)
 
 	/* Add myself to the wait queue. */
 	SpinLockAcquire(&cv->mutex);
-	proclist_push_head(&cv->wakeup, pgprocno, cvWaitLink);
+	if (!proclist_contains(&cv->wakeup, pgprocno, cvWaitLink))
+		proclist_push_head(&cv->wakeup, pgprocno, cvWaitLink);
 	SpinLockRelease(&cv->mutex);
 }
 
@@ -100,7 +101,8 @@ ConditionVariableCancelSleep(void)
 		return;
 
 	SpinLockAcquire(&cv->mutex);
-	proclist_delete(&cv->wakeup, MyProc->pgprocno, cvWaitLink);
+	if (proclist_contains(&cv->wakeup, MyProc->pgprocno, cvWaitLink))
+		proclist_delete(&cv->wakeup, MyProc->pgprocno, cvWaitLink);
 	SpinLockRelease(&cv->mutex);
 
 	MyProc->cvSleeping = false;
@@ -126,6 +128,7 @@ ConditionVariableSignal(ConditionVariable *cv)
 	/* If we found someone sleeping, set their latch to wake them up. */
 	if (proc != NULL)
 	{
+		proc->cvSleeping = false;
 		SetLatch(&proc->procLatch);
 		return true;
 	}
diff --git a/src/include/storage/proclist.h b/src/include/storage/proclist.h
index 0d7935c..b14e8f8 100644
--- a/src/include/storage/proclist.h
+++ b/src/include/storage/proclist.h
@@ -69,6 +69,8 @@ proclist_push_head_offset(proclist_head *list, int procno, size_t node_offset)
 	else
 	{
 		Assert(list->tail != INVALID_PGPROCNO);
+		Assert(list->head != procno);
+		Assert(list->tail != procno);
 		node->next = list->head;
 		proclist_node_get(node->next, node_offset)->prev = procno;
 		node->prev = INVALID_PGPROCNO;
@@ -77,7 +79,7 @@ proclist_push_head_offset(proclist_head *list, int procno, size_t node_offset)
 }
 
 /*
- * Insert a node a the end of a list.
+ * Insert a node at the end of a list.
  */
 static inline void
 proclist_push_tail_offset(proclist_head *list, int procno, size_t node_offset)
@@ -93,6 +95,8 @@ proclist_push_tail_offset(proclist_head *list, int procno, size_t node_offset)
 	else
 	{
 		Assert(list->head != INVALID_PGPROCNO);
+		Assert(list->head != procno);
+		Assert(list->tail != procno);
 		node->prev = list->tail;
 		proclist_node_get(node->prev, node_offset)->next = procno;
 		node->next = INVALID_PGPROCNO;
@@ -117,6 +121,38 @@ proclist_delete_offset(proclist_head *list, int procno, size_t node_offset)
 		list->tail = node->prev;
 	else
 		proclist_node_get(node->next, node_offset)->prev = node->prev;
+
+	node->next = node->prev = INVALID_PGPROCNO;
+}
+
+/*
+ * Check if a node is currently in a list.  It must be known that the node is
+ * not in any _other_ proclist that uses the same proclist_node, so that the
+ * only possibilities are that it is in this list or none.
+ */
+static inline bool
+proclist_contains_offset(proclist_head *list, int procno,
+						 size_t node_offset)
+{
+	proclist_node *node = proclist_node_get(procno, node_offset);
+
+	/*
+	 * If this node has never been a member of a cv list, then it will contain
+	 * zero before and after us in the list.  Circular lists are not allowed
+	 * so this condition is not confusable with a real pgprocno 0.
+	 */
+	if (node->prev == 0 && node->next == 0)
+		return false;
+
+	/* If there is a previous node, then this node must be in the list. */
+	if (node->prev != INVALID_PGPROCNO)
+		return true;
+
+	/*
+	 * There is no previous node, so the only way this node can be in the list
+	 * is if it's the head node.
+	 */
+	return list->head == procno;
 }
 
 /*
@@ -145,6 +181,8 @@ proclist_pop_head_node_offset(proclist_head *list, size_t node_offset)
 	proclist_push_tail_offset((list), (procno), offsetof(PGPROC, link_member))
 #define proclist_pop_head_node(list, link_member) \
 	proclist_pop_head_node_offset((list), offsetof(PGPROC, link_member))
+#define proclist_contains(list, procno, link_member) \
+	proclist_contains_offset((list), (procno), offsetof(PGPROC, link_member))
 
 /*
  * Iterate through the list pointed at by 'lhead', storing the current